Sleep and fainting: possible causes

Fainting usually involves a brief loss of consciousness followed by recovery. It can follow standing quickly, overheating, pain, fear, dehydration, or a drop in blood glucose. Anaemia may reduce oxygen delivery and Atrial Fibrillation or another rhythm problem may affect circulation. Fainting while lying down, during exertion, with palpitations, or without warning deserves particular attention because a heart-related cause needs to be considered. A dream, sleep movement, or waking sensation does not by itself explain the event.

If you feel faint, lie flat and raise your legs if safe, or sit with your head lowered. Move away from heat, loosen clothing, and take slow breaths. Once fully alert, drink fluids and eat if you may have gone without food, unless a clinician has told you to restrict either. Someone who has fainted should be checked for injury and observed until recovered. Record posture, warning symptoms, food, fluids, medicines, palpitations, and the length of recovery.

Call emergency services for fainting with chest pain, severe breathlessness, a sustained fast or irregular heartbeat, seizure-like activity, serious injury, pregnancy, or failure to wake promptly. Get urgent assessment when fainting occurs during exercise, while lying down, repeatedly, or with weakness, speech trouble, severe headache, or new confusion. Arrange a medical appointment for any unexplained episode.

Ask whether you need blood pressure checks lying and standing, blood tests, or an electrocardiogram. Explain what happened before and after the blackout, whether anyone saw it, and whether medicines, dehydration, skipped meals, or a family history of heart rhythm problems may be relevant.