7 Signs of Heat Exhaustion You Should Never Ignore

Between 2012 and 2022, extreme heat sent more than 7,000 Australians to hospital and was linked to almost 300 deaths – and heatwaves caused more injury hospitalisations than any other extreme weather event in that decade.

Yet many of us still shrug off feeling dizzy, nauseous or “cooked” after a day in the Aussie sun.

Maybe you’ve pushed through a blazing afternoon on site, a summer netball game, or a long drive in a car with patchy air-con – telling yourself you just need to “harden up”, have a drink and you’ll be fine.

The problem? Those early heat exhaustion symptoms are exactly what can snowball into life‑threatening heat stroke if you ignore them.

In this article, we’ll break down:

• What heat exhaustion actually is (and how it differs from heat stroke)
• The 7 key signs of heat exhaustion you should never ignore
• How to respond quickly at home or work
• When it’s time to call triple zero (000)
• When it’s appropriate to talk to a GP or telehealth doctor instead
• Simple summer health safety habits to protect yourself and your family this year

We’ll draw on Australian sources like Healthdirect, state and territory health departments and the Australian Institute of Health and Welfare, and we’ll also explain where we at NextClinic can (and cannot) safely help via telehealth if you’re unwell in the heat.

By the end, you’ll know the difference between “a bit hot and bothered” and the kind of symptoms that deserve action – not bravado.

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Why heat exhaustion is a serious issue in Australia

Australia is getting hotter, and our summers are getting harsher.

National data show that extreme heat is responsible for the majority of weather‑related injury hospitalisations in Australia – around 7,104 hospitalisations and 293 deaths over a recent 10‑year period, making heatwaves our most dangerous natural hazard in terms of loss of life.

Recent summers and El Niño years have seen repeated spikes in extreme heat cases, with more than 1,000 hospitalisations in peak years.

And it’s not just the outback.

• Western Sydney regularly records temperatures in the high 30s to 40s.
• Many older homes and rentals across our cities have poor insulation or no air‑con.
• Outdoor workers, athletes, small kids, older Australians and people with chronic illness are especially at risk.

In other words: if you live in Australia, heat exhaustion is not a fringe problem. It’s something that can affect you on a beach day, at a summer festival, during a heatwave at home, or even in a hot warehouse or commercial kitchen.

Heat exhaustion vs heat stroke: what’s the difference?

Understanding the difference between heat exhaustion and heat stroke is crucial, because the treatment – and urgency – is very different.

Heat exhaustion (serious, but usually reversible)

Heat exhaustion happens when:

• You’ve overheated and
• You’re becoming dehydrated and losing salts through sweat faster than you can replace them.

Your core body temperature may be up, but usually not to dangerous levels yet. If you act quickly – cool down, rehydrate and rest – you can often prevent the situation from escalating.

Typical heat exhaustion symptoms include:

• Heavy sweating, pale or clammy skin
• Dizziness or feeling light‑headed
• Headache
• Nausea or vomiting
• Muscle cramps
• Weak, rapid pulse
• Extreme thirst and other dehydration symptoms

We’ll unpack these in more detail shortly.

Heat stroke (a medical emergency)

Heat stroke is at the extreme end of the spectrum. It happens when your body can no longer control its temperature – usually with a core temperature of 40°C or more – and vital organs start to struggle.

Typical heat stroke signs include:

• Body temperature 40°C or higher
• Hot, red skin (may be dry or very sweaty)
• Confusion, agitation, slurred speech or acting strangely
• Seizures, collapse or loss of consciousness
• Rapid, shallow breathing and a very fast pulse

Heat stroke is a medical emergency. Healthdirect, state health departments and the NT Government all advise calling triple zero (000) immediately if you suspect heat stroke or if heat exhaustion symptoms are severe or not improving.

This article focuses on catching the earlier, treatable signs of heat exhaustion – but we’ll keep flagging when a symptom tips over into “call an ambulance now” territory.

The 7 signs of heat exhaustion you should never ignore

Most people don’t experience just one symptom in isolation. Heat exhaustion often feels like a cluster of warning signs building over minutes to hours.

Here are seven key signs you shouldn’t brush off, especially in the Aussie summer.

1. Thirst, dark urine and other dehydration symptoms

We talk a lot about “staying hydrated”, but dehydration can creep up faster than you think – particularly in heatwaves, during exercise or when you’re on certain medications.

According to Healthdirect, common dehydration symptoms include:

• Feeling very thirsty
• Dry mouth, lips and tongue
• Feeling dizzy, especially when standing up
• Headache
• Dark yellow urine or not peeing much
• Feeling tired or irritable

In the context of hot weather, these dehydration signs and heat exhaustion symptoms often overlap. If you’re outdoors on a 35°C day and realise you haven’t peed for hours – or your urine is dark and strong‑smelling – that’s your body waving a red flag.

Don’t ignore it if:

• You can’t keep fluids down due to vomiting
• You feel faint, confused or extremely weak
• A baby or elderly person hasn’t had a wet nappy or been to the toilet for a long time

These are situations where you should seek urgent medical help – call 000 for severe symptoms, or contact Healthdirect (1800 022 222) or a doctor straight away for advice.

2. Dizziness, light‑headedness or fainting

Feeling woozy when you stand up after sitting in the heat all afternoon is not something to tough out.

Dizziness or fainting in hot weather can result from:

• Lower blood pressure as your blood vessels dilate to help you cool
• Dehydration reducing your circulating blood volume
• Your brain not quite getting enough oxygenated blood when you change position

Australian hot‑weather guidelines list dizziness and fainting among classic signs of heat‑related illness that should prompt urgent attention.

Act fast if:

• You feel light‑headed, especially when standing
• You have to sit or lie down to stop yourself blacking out
• Someone actually faints in the heat

Move to a cool, shaded or air‑conditioned area, lie down (ideally with legs slightly raised), loosen clothing and sip cool water if the person is awake and able to drink. If they don’t perk up quickly, or you’re worried at all, call 000.

3. Heavy sweating with pale, cool, clammy skin

Sweating is your body’s built‑in air‑con. Under normal circumstances, sweat evaporating off your skin helps cool you down.

In heat exhaustion, though, the system is struggling:

• You may be sweating heavily, but still overheating.
• Skin can look pale, cool and clammy, even though the environment is hot.

NT Health and other Australian resources specifically describe profuse sweating and clammy, pale skin as classic features of heat exhaustion.

Why it matters:

• You’re losing large amounts of fluid and salts.
• If you don’t replace them, your circulation and muscles start to suffer.
• Left unchecked, this can tip over into heat stroke, where sweating may actually decrease and skin becomes dry and very hot.

If you’re drenched in sweat but not cooling down, stop what you’re doing. Rest in a cool area, drink water or an oral rehydration fluid, and use cool cloths, mist sprays or a cool shower to help your body catch up.

4. Headache that worsens in the heat

Headaches are easy to dismiss – we blame screen time, stress, or “just being tired”. But in summer, especially during a heatwave, headache can be an early heat exhaustion symptom.

Heat‑related headaches often:

• Build gradually as you spend more time in the heat
• Come with other symptoms like thirst, dizziness or nausea
• Improve once you cool down and rehydrate

Remember that dehydration alone is a well‑recognised trigger for headache.

Red flags with headache in the heat:

• Confusion, difficulty speaking or understanding
• Weakness in the face, arm or leg (particularly on one side)
• Sudden, extremely severe “worst ever” headache
• Stiff neck, fever or a rash

Those are emergencies that could indicate stroke, meningitis or other serious conditions – call 000 immediately.

For more typical heat‑related headaches that settle once you’re cooled and hydrated, it can still be wise to check in with a GP or telehealth doctor, particularly if:

• You get frequent migraines that seem triggered by hot weather
• You need a medical certificate for work or study
• Your headache pattern has changed suddenly

We often see patients at NextClinic who need to take a sick day during a heatwave due to migraine or heat‑related symptoms. If your situation is non‑emergency, one of our doctors can assess you via telehealth and, if appropriate, issue a medical certificate online so you can rest and recover.

5. Nausea, vomiting or loss of appetite

Feeling sick in the heat is another sign many people push through – especially at outdoor events or parties.

Nausea and vomiting can be caused by:

• Dehydration and electrolyte imbalance
• Reduced blood flow to the gut as your body redirects blood to the skin
• Direct effects of high body temperature

NT Health and other state resources list nausea and/or vomiting among key symptoms of heat exhaustion and heat stress.

Take it seriously if:

• You can’t keep fluids down
• Vomiting is ongoing or severe
• There’s any confusion, chest pain, or collapse along with the vomiting

Vomiting quickly worsens dehydration and can accelerate progression from heat exhaustion to heat stroke. If you (or someone you’re with) is vomiting repeatedly in hot conditions, don’t just wait it out – call 000 for severe symptoms, or seek urgent medical care.

6. Muscle cramps, weakness and feeling “wiped out”

If you’ve ever had a calf or hamstring cramp after training in the summer heat, you’ve felt how painful heat cramps can be.

Heat‑related muscle cramps and weakness usually occur because:

• You’re sweating out large amounts of salt and fluid
• Your muscles are working hard (e.g. sport, labouring, tradie work)
• You haven’t replaced enough electrolytes

Weakness, fatigue and restlessness feature prominently in government descriptions of heat exhaustion.

What to do:

• Stop the activity and rest in a cool place.
• Gently stretch and massage the affected muscles once pain allows.
• Sip cool water or an oral rehydration solution – avoid alcohol and excessive caffeine, which can worsen fluid loss.

If muscle cramps or weakness don’t improve after you’ve cooled down and rehydrated, or they keep recurring with only light activity in the heat, it’s time to talk to a doctor – especially if you have heart or kidney disease, diabetes or are on diuretics or other medications that affect fluid balance.

A telehealth doctor can help assess whether your symptoms sound like simple heat exhaustion, a medication side effect, or something needing in‑person tests.

7. Fast heartbeat and rapid breathing

As your body struggles with heat, your heart and lungs often work harder to:

• Get blood to the skin for cooling
• Maintain blood pressure despite fluid loss
• Deliver enough oxygen to overheated tissues

Heat exhaustion can show up as:

• A fast but weak pulse
• Rapid breathing
• Feeling your heart racing or pounding, especially when you stand or walk a short distance

This is not something to ignore, particularly if you also feel:

• Chest pain or tightness
• Short of breath at rest
• Light‑headed or on the verge of fainting

These can be signs of serious cardiovascular strain.

Heatwaves are known to worsen heart and kidney problems and are linked to increased deaths from cardiovascular and respiratory causes – especially in older adults and people with pre‑existing disease.

Call 000 immediately if you or someone near you develops:

• Chest pain
• Severe shortness of breath
• A very fast or irregular heartbeat that doesn’t settle quickly
• Collapse or loss of consciousness

When heat exhaustion turns into heat stroke: the red‑flag signs

By now you can see that heat‑related illness sits on a spectrum.

If you don’t respond promptly to early heat exhaustion symptoms, they can progress to heat stroke, which is life‑threatening.

Australian guidance (including Healthdirect and state health departments) emphasises seeking urgent help if you notice:

• Body temperature 40°C or higher
• Hot, red skin (may be dry or very sweaty)
• Confusion, agitation, slurred speech or acting “not themselves”
• Seizures, collapse or loss of consciousness
• Very fast pulse and rapid, shallow breathing
• Stopping sweating despite the heat

In these situations:

1. Call triple zero (000) immediately and ask for an ambulance.
2. Move the person to a cool, shaded or air‑conditioned place.
3. Remove excess clothing.
4. Cool them rapidly with cool water (sprays, wet towels, a cool shower if conscious) and fans or air movement.
5. Place cold packs on the neck, armpits and groin if available.
6. If they’re unconscious but breathing, place them on their side and keep cooling them until help arrives.

Do not rely on painkillers like paracetamol or ibuprofen to “bring the temperature down” in suspected heat stroke – they don’t treat the underlying problem and can be harmful. Cooling the body and urgent medical care are what matter.

This is not a time for telehealth or self‑care at home; it’s an emergency.

Who is most at risk from heat exhaustion in Australia?

Anyone can get heat exhaustion or heat stroke, but some groups are particularly vulnerable in our climate. Australian government hot‑weather advice highlights:

• Babies and young children – they heat up faster and can’t always say how they feel.
• Older adults, especially those living alone or with limited mobility.
• People with chronic health conditions – such as heart disease, lung disease, kidney problems, diabetes or mental health conditions.
• Pregnant and breastfeeding women.
• People taking certain medications – like diuretics (“fluid tablets”), some blood pressure medications, some antidepressants or antipsychotics, and drugs that affect sweating or fluid balance.
• Outdoor workers – tradies, agricultural workers, road crews, landscapers, lifeguards, etc.
• Athletes and very active people – including weekend warriors doing long runs, footy training or bootcamps in hot weather.
• People in poorly cooled housing – such as older units, social housing or homes without air‑conditioning.

If you or a family member fall into one of these groups, it’s worth having a summer health safety plan:

• How will you keep the house cool on 40°C days?
• Who will check in on elderly relatives or neighbours?
• What are your workplace’s heat policies if you work outdoors?
• Which doctor's number (or telehealth service) will you call if someone starts to feel unwell?

First aid: what to do if you suspect heat exhaustion

If you catch heat exhaustion early, simple steps can often reverse it and prevent deterioration.

Australian health authorities (including Healthdirect, NT Health and ACT/NSW guidelines) generally recommend:

1. Move to a cooler place
   • Indoors with air‑conditioning if possible
   • Or at least a shaded, well‑ventilated area outdoors
2. Lie down and rest
   • Loosen or remove heavy clothing
   • If feeling faint, lying on your back with legs slightly raised can help blood flow to the brain
3. Rehydrate
   • Take small, frequent sips of cool water
   • Oral rehydration solutions or sports drinks (in moderation) can help replace electrolytes
   • Avoid alcohol, and go easy on caffeine
4. Cool the body
   • Take a cool (not icy‑cold) shower or bath
   • Or sponge/spray the skin with cool water and use a fan
   • Place cool packs or damp cloths on the neck, armpits and groin
5. Stay with the person
   • Don’t leave someone with heat exhaustion alone, especially if they’re drowsy or unsteady.
6. Seek medical advice if not improving quickly
   • If symptoms are not clearly improving within 30 minutes,
   • Or any red‑flag signs appear (confusion, chest pain, vomiting that won’t stop, collapse, seizure, temperature 40°C or more),

call 000 or go straight to an emergency department.

If symptoms are mild, have improved with rest and cooling, but you still feel washed out or unsure what to do next, that’s a good time to call Healthdirect, your usual GP, or speak to a telehealth doctor for personalised advice.

Summer health safety: how to prevent heat exhaustion and heat stroke

Prevention really is better than cure when it comes to heat.

Australian hot‑weather guidelines and Healthdirect recommend a few core strategies:

1. Drink regularly – don’t wait until you’re thirsty

• Aim to sip water throughout the day, especially in hot weather or when you’re active.
• Take a bottle with you whenever you leave the house.
• Limit alcohol and sugary drinks – they can worsen dehydration.
• If you’re on fluid restrictions for a medical condition, discuss a personalised plan with your doctor before summer.

2. Keep your environment cool

• Use fans or air‑conditioning if you have them.
• Close curtains and blinds during the hottest part of the day.
• Use shade cloth, awnings or external blinds where possible.
• If your home gets dangerously hot, spend the hottest hours (often 11am–3pm) in cooler public places like libraries, shopping centres or community centres.

3. Time your outdoor activity

• Avoid strenuous activity in the middle of the day.
• Plan exercise, yard work or kids’ sport for early morning or later in the evening.
• If you must work outdoors, take regular breaks in the shade and drink often.

4. Dress for the weather

• Wear light‑coloured, loose‑fitting clothing made of breathable fabrics like cotton.
• Use a broad‑brimmed hat, sunglasses and SPF 30+ or higher sunscreen for sun protection.
• For sports, choose moisture‑wicking fabrics that allow sweat to evaporate.

5. Look after those at higher risk

• Check on older relatives, neighbours and people with disabilities during heatwaves.
• Keep children cool, offer them water frequently, and never leave kids or pets in parked cars – even for a few minutes.
• Ensure pets also have shade and plenty of fresh water.

6. Be heat‑aware if you take regular medications

Some medicines – including certain blood pressure tablets, diuretics, some psychiatric medicines and even some hormonal treatments – can affect how your body handles heat or fluids.

If you’re unsure how your medication interacts with hot weather:

• Ask your usual GP or pharmacist
• Or speak with a telehealth doctor in Australia for advice before the next heatwave

At NextClinic, we can’t change every type of medication online, but we can often help with reviewing your general situation, arranging an in‑person review when needed, or providing safe online prescriptions and specialist referrals where appropriate.

When to see a GP or telehealth doctor about heat exhaustion

Not every heat‑related episode needs an ambulance – but it does deserve medical attention more often than many Australians think.

Consider seeing a GP or telehealth doctor if:

• You’ve had a recent episode of heat exhaustion, even if you recovered at home.
• You keep getting dizzy, wiped out or nauseous when it’s hot.
• You have heart, kidney or lung disease and have felt worse in recent heatwaves.
• You’re on regular medications and are unsure how to manage them during hot weather.
• You need time off work or study to recover and require a medical certificate.

How NextClinic can help (and where we draw the line)

As a telehealth startup based in Australia, we’re here to support – not replace – emergency care.

Through our online platform, our Australian‑registered doctors can:

• Assess your symptoms via phone for non‑emergency concerns
• Provide advice on managing mild heat exhaustion at home
• Review your medications and suggest follow‑up with your usual GP where necessary
• Issue online medical certificates for sick leave if you’re unfit for work or study, when clinically appropriate
• Provide online prescriptions for certain regular or short‑term medications, if it’s safe to do so
• Arrange specialist referrals (for example, to a cardiologist or respiratory physician) if your heat symptoms raise concerns that need further investigation

You can learn more about:

• How our telehealth consultations work on our Telehealth Consultation page
• What makes a valid online medical certificate in our blog post on online medical certificates

However, there are clear situations where telehealth – including NextClinic – is not appropriate:

• Suspected heat stroke or rapidly worsening heat exhaustion
• Chest pain, severe shortness of breath or collapse
• Confusion, seizures or loss of consciousness
• Children or vulnerable adults who appear very unwell

In those cases, do not book an online consultation. Call 000 or attend your nearest emergency department or urgent care service immediately.

Bringing it all together – and your challenge for this week

Let’s recap the key takeaways:

• Heat exhaustion is common – and dangerous if ignored. In Australia, extreme heat leads to more weather‑related hospitalisations than any other hazard.
• Heat exhaustion and heat stroke are not the same. Heat exhaustion is serious but usually reversible; heat stroke is life‑threatening and always an emergency.
• The 7 signs of heat exhaustion you should never ignore are:
  1. Thirst, dark urine and other dehydration symptoms
  2. Dizziness, light‑headedness or fainting
  3. Heavy sweating with pale, cool, clammy skin
  4. Headache that worsens in the heat
  5. Nausea, vomiting or loss of appetite
  6. Muscle cramps, weakness and feeling wiped out
  7. Fast heartbeat and rapid breathing
• Red‑flag heat stroke signs – high body temperature, confusion, collapse, seizures, hot red skin – mean you must call 000 straight away.
• Smart summer health safety habits – hydrating regularly, keeping your home cool, avoiding peak heat, dressing for the weather and checking on vulnerable people – go a long way towards prevention.
• A telehealth doctor can be a safe, convenient option for non‑emergency heat‑related issues, follow‑up, medication reviews, and legitimate online medical certificates when you’re too unwell to make it into a clinic.

Your challenge

This week, pick one concrete action from this article and actually do it:

• Maybe it’s setting a reminder on your phone to drink water every hour during work.
• Maybe it’s talking to your manager about safer break schedules on extreme heat days.
• Maybe it’s planning how you’ll check on elderly relatives during the next heatwave.
• Or printing emergency numbers and sticking them on the fridge so the whole family knows what to do.

Then, we’d love to hear from you:

Which strategy are you going to try – and how did it go? Share your experience in the comments or send us a message. Your story might be the nudge someone else needs to take heat exhaustion seriously this summer.

Stay cool, stay safe – and if you’re ever unsure, reach out to a doctor, whether that’s your local GP or one of our team here at NextClinic.

References

• Extreme weather is leading to more injury hospitalisations, with heat being the main cause - Australian Institute of Health and Welfare
• Australia's health 2024: data insights: Extreme weather related injuries in Australia over the last decade - Australian Institute of Health and Welfare
• Hot weather safety | NSW Government
• Hot weather risks and staying cool | healthdirect
• Heatstroke | healthdirect
• Dehydration - signs, symptoms and treatment | healthdirect
• Heat stress | NT.GOV.AU
• Online Medical Certificate | NextClinic
• Heatwaves caused more than 1,000 deaths in Australia over four-year period, study finds
• Online Doctors: Telehealth Consultations at NextClinic
• Instant Scripts Available at NextClinic | NextClinic
• How to Fast-Track Your Specialist Referral | NextClinic

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