What causes postural syncope?

Standing can cause blood to pool in the legs. If the body does not compensate quickly enough, blood flow to the brain may fall briefly and cause fainting. Dehydration, overheating, blood loss, Anaemia, low blood sugar, medicine effects and heart-rhythm problems such as Atrial Fibrillation can contribute. The circumstances matter: fainting during exercise, while lying down, or with palpitations needs particular attention. One episode does not establish the cause.

Lie flat and raise your legs if comfortable, then remain still until fully alert. Do not drive, climb or return to risky activity immediately. Drink fluids if you are awake and able to swallow, unless a clinician has restricted your intake. Make a note of warning symptoms, position, heat, food, recent illness and medicines. Arrange assessment after any unexplained faint, especially if it recurs or caused an injury.

Call emergency services if the person does not wake promptly, has difficulty breathing, chest pain, a serious injury, seizure-like movements, new weakness, trouble speaking or a persistent irregular heartbeat. Urgent assessment is also needed when fainting occurs during exertion, without warning, or while lying down.

Ask whether blood pressure and pulse should be checked lying and standing, whether an ECG or blood tests are appropriate, and whether any medicine, fluid restriction or missed meal could have contributed.