Heat syncope: causes

Heat syncope is fainting or near-fainting caused by heat, standing, blood pooling, and reduced circulation to the brain. Sweating lowers circulating fluid, while widened skin blood vessels send more blood toward the surface for cooling.

The risk rises after standing still, changing position quickly, exercising, or becoming dehydrated. Other explanations can include anaemia, an irregular rhythm such as atrial fibrillation, or low blood sugar. These possibilities need assessment rather than self-diagnosis.

Help the person lie flat in a cool place and raise the legs if there is no injury. Loosen tight clothing, offer small sips of fluid only when they are fully awake, and let them recover gradually. Avoid standing suddenly or returning to heat until they feel steady.

Arrange urgent help for chest pain, breathlessness, a racing or irregular heartbeat, injury, seizure, prolonged unresponsiveness, or fainting during exercise. Medical review is also sensible after a first episode, repeated episodes, or fainting without a clear heat trigger.

Ask whether you need a heart rhythm check, blood tests, a medication review, or advice about hydration and safe activity in hot weather.