Fainting out of nowhere: when to get help

Some people notice no warning before consciousness briefly stops. A heart-rhythm disturbance may reduce blood flow quickly; other causes include dehydration, anaemia, low blood sugar or a blood-pressure drop. A witness can provide useful details, such as pallor, movements, breathing and how quickly normal awareness returned.

Have someone check that you are breathing and call emergency services if you do not wake promptly. If you are breathing, lie flat with your legs raised and avoid standing until steady. Do not drive, climb or operate machinery while the cause is unexplained. Write down the circumstances and medicines involved.

Emergency care is needed for chest pain, breathlessness, palpitations, severe headache, new weakness, speech trouble, seizure-like activity, major injury, fainting during exercise or a family history of sudden cardiac death. Even without these signs, arrange prompt review when fainting had no warning or has happened more than once.

Ask whether you need lying and standing blood-pressure readings, an ECG or blood tests. Mention any new medicine, illness, skipped meal, fluid loss, pregnancy possibility, family heart history and the witness account.