What should you know about heart rate when fainting?

A brief drop in blood pressure can reduce blood flow to the brain and may happen after standing, heat, pain, fear or prolonged sitting. Dehydration, anaemia and low blood sugar can contribute. Some fainting episodes are preceded by a faster pulse, sweating, nausea or warmth; others involve a slow pulse. An irregular rhythm such as atrial fibrillation is a possible medical cause, particularly when fainting happens suddenly or without warning. A clinician may need the circumstances, examination, blood tests and an electrocardiogram to assess the event.

Lay the person flat and raise the legs if there is no injury and breathing is normal. Loosen tight clothing, keep the area safe and stay with them. Do not give food or drink until they are fully awake. If they are not breathing normally, begin emergency first aid and follow the emergency operator's instructions. Once recovered, avoid driving, heights and swimming alone until assessed.

Call emergency services if the person does not wake promptly, has trouble breathing, chest pain, a severe headache, prolonged confusion, a serious injury, seizure-like movements, or fainted during exertion. Urgent assessment is also needed for a first unexplained episode, repeated fainting, fainting while lying down, or a known heart condition.

Ask whether the event sounds like fainting or another cause of collapse, whether you need an electrocardiogram or rhythm monitor, and whether medicines, fluid intake, blood sugar or anaemia should be reviewed. Bring a witness account if available.