Why Heat Makes You Sleepy

Quick answer

Hot weather can leave you feeling tired because your body is working to cool itself, especially when you are active or losing fluid through sweat. A hot night can also disrupt sleep. But unusual weakness, dizziness or confusion in the heat can signal illness and should not be dismissed as ordinary sleepiness.

Why heat can make you feel tired

To cool down, the body sends more blood toward the skin and produces sweat. Heat exposure, exertion and fluid loss can contribute to fatigue, and individual responses vary with health, medications, humidity and activity. A poor night’s sleep in a hot room may add to daytime tiredness; sleepiness does not have one universal cause.

Heat exhaustion and heat stroke

Heat exhaustion can include heavy sweating, weakness, headache, dizziness, nausea and thirst. Move to a cooler place, loosen clothing, cool the person with wet cloths and offer sips of water if they are fully awake and can swallow. Seek medical attention if symptoms worsen, vomiting occurs or symptoms last longer than an hour. See the CDC’s heat-illness guidance.

Heat stroke is an emergency. Confusion, slurred speech, seizures, fainting or loss of consciousness in the heat can be warning signs. Call 911 immediately, move the person to a cooler place and begin cooling with cold wet cloths or a cool bath while help is coming. Do not give an unconscious or confused person anything to drink. Skin may be dry or sweaty; do not wait for sweating to stop.

How to sleep more comfortably in hot weather

• Use air conditioning if available or seek an air-conditioned place when your home is dangerously hot.
• Choose lighter bedding and comfortable clothing; use a cool, damp cloth or shower if that helps you feel comfortable.
• Use a fan only when conditions make it safe. The CDC advises against relying on fans when indoor temperatures are above 90°F, because they can increase body temperature.
• Drink water regularly in hot weather unless a clinician has advised a fluid restriction. Avoid relying on alcohol for hydration.

Bedroom temperature preferences differ. A mattress or sheet label alone cannot guarantee that you will sleep cool.

When to look beyond the weather

Persistent daytime sleepiness, loud snoring with gasping or breathing pauses, or frequent unrefreshing sleep deserves a conversation with a healthcare professional. If symptoms occur during heat exposure, assess for heat illness rather than assuming a sleep problem.