Heat exhaustion at night: what to know and do

A hot bedroom, heavy bedding, outdoor activity earlier in the day or limited access to fluids can prevent the body from shedding heat effectively. Sweating removes water and salts, so fluid loss may continue even after you lie down. Symptoms can include heavy sweating, weakness, headache, nausea, muscle cramps, thirst, cool or clammy skin and dizziness. Dehydration may occur alongside heat exhaustion; dark urine and a dry mouth can suggest that you need more fluid.

Night-time symptoms can also have other causes, and a thermometer reading does not by itself establish the diagnosis. Pay attention to the setting, recent exertion, medicines, alcohol intake and whether symptoms improve after cooling.

Move to the coolest available room or a shaded, ventilated place. Stop activity, loosen or remove extra clothing, and lie down with the legs comfortably raised if you feel faint. Apply cool, damp cloths to the skin or use a fan; a cool shower may help if you are alert and steady enough to use it safely.

Take frequent small sips of cool water. An oral rehydration drink may be useful when sweating has been substantial, provided you can drink safely. Avoid alcohol and strenuous activity while recovering. Stay with the person and reassess whether alertness, dizziness and nausea are improving.

Call emergency services if the person becomes confused, has a seizure, faints, cannot drink, has trouble breathing, or is very hot with altered alertness. These features may indicate a more dangerous heat illness. Do not give fluids to someone who is confused, vomiting repeatedly or unable to swallow, and do not leave them alone.

Seek urgent medical advice if symptoms are worsening, do not improve after cooling and drinking, or return repeatedly at night. Arrange a clinical review for ongoing heat intolerance, repeated dizziness, persistent vomiting, or suspected dehydration, especially in a child, older adult, pregnant person or someone with a long-term illness.

Ask whether a medicine, illness or sleep environment could be increasing your risk of heat-related symptoms. Tell the clinician when symptoms begin, how much you were sweating, what you drank, whether you had dark urine or dizziness, and how quickly cooling changed the symptoms.