What causes fainting?

Some people feel warm, sweaty, nauseated, light-headed, or see spots before fainting. Standing quickly can trigger postural hypotension, while prolonged standing, emotional distress, pain, or seeing blood can activate a reflex that slows the heart and widens blood vessels. Dehydration, heat stroke, low blood sugar, and anaemia can reduce the body's ability to maintain circulation. Fainting during exertion, while lying down, or with palpitations raises concern about a heart cause. A seizure can look similar but may involve prolonged confusion, tongue injury, or rhythmic jerking.

Tell a clinician what happened before, during, and after the event, including injuries, medicines, food and fluid intake, and whether anyone saw it.

Lie flat and raise the legs if possible, loosen tight clothing, and stay still until fully alert. Do not stand suddenly or drive until the cause has been assessed. If someone faints, check breathing, protect them from injury, and place them on their side if they are vomiting or not fully awake. Arrange medical review after an unexplained episode, a first episode, or repeated fainting.

Call emergency services if the person is not breathing normally, does not wake promptly, has chest pain, severe breathlessness, a fast or irregular heartbeat, new weakness, serious injury, or fainting during exercise. Urgent assessment is also needed when fainting occurs with pregnancy, bleeding, severe dehydration, suspected heat stroke, or a possible seizure.

Could my medicines, blood pressure, blood sugar, blood count, or heart rhythm explain this? Do I need an ECG or other checks? What activities should I avoid until review?