syncope

Syncope is a sudden, brief loss of consciousness caused by a temporary drop in blood flow to the brain, followed by a full and spontaneous recovery. In plain terms it is fainting: the brain, deprived of oxygen for a few seconds, switches off, the person collapses, and — because lying flat restores blood to the head — usually comes round within moments looking pale and shaken but soon back to normal.

The common, mostly benign form is reflex or vasovagal syncope, where a trigger such as pain, fear, the sight of blood, or prolonged standing causes the nervous system to abruptly slow the heart and widen blood vessels, dropping blood pressure. Another group comes from orthostatic causes — standing up too fast when fluid-depleted or on certain medicines. The most worrying group is cardiac syncope, where a fast or slow arrhythmia, a blocked valve, or another heart problem cuts output without warning.

Sorting these out matters because cardiac syncope carries a higher risk of sudden death and demands thorough investigation, whereas reflex syncope is usually reassuring once dangerous causes are excluded. Red flags include fainting during exertion, fainting with no warning while seated or lying down, palpitations beforehand, or a family history of sudden death.