Having a blackout: what you should know

Fainting, also called syncope, may happen after standing for a long time, sudden pain, fear, overheating, or not drinking enough. Some people feel light-headed, sweaty, nauseated, weak, or notice blurred vision before they lose consciousness. Recovery is often quick, but tiredness or confusion can follow.

A blackout can also have a heart-related cause, a blood-pressure problem, low blood sugar, or another medical explanation. Anaemia, dehydration, hypoglycaemia, and atrial fibrillation are examples of conditions a clinician may consider alongside your medicines, medical history, and what happened immediately before the episode.

If you feel a blackout coming, lie down and raise your legs if you can. If someone has fainted, place them on their back, check that they are breathing, loosen tight clothing, and keep the area clear. Do not give food or drink until they are fully awake. Turn them onto their side if they are vomiting or not fully alert, and stay with them.

Afterward, write down the activity, posture, symptoms beforehand, possible triggers, injuries, and how quickly normal awareness returned. Arrange a medical review for a first unexplained episode, any recurrence, or an episode that happened during exertion or while sitting or lying down.

Call emergency services if the person does not wake promptly, is not breathing normally, has severe chest pain, severe breathlessness, a persistent irregular heartbeat, a seizure, serious injury, or new weakness or difficulty speaking. Urgent assessment is also needed when fainting occurs during exercise, follows a head injury, happens without warning, or affects someone with known heart disease.

Do not drive until a clinician has advised you after a blackout. If you are pregnant, have diabetes, take medicines that affect blood pressure or heart rhythm, or have repeated episodes, seek medical advice promptly even if you feel recovered.

Ask what checks are appropriate, whether your medicines or hydration may contribute, and whether you need an ECG or blood tests. Tell the clinician whether anyone saw shaking, unusual movements, tongue biting, loss of bladder control, or prolonged confusion, because these details can help distinguish fainting from other causes of lost awareness.