Low blood pressure and passing out: what to know

Fainting is a brief loss of consciousness followed by recovery. It can happen after standing quickly, prolonged standing, heat exposure, dehydration, pain or illness. Warning sensations may include dimming vision, nausea, sweating, weakness or ringing in the ears. A fall can cause injury even when the underlying episode is short.

Passing out is not automatically explained by a low blood-pressure reading. Heart rhythm problems, bleeding, low blood sugar, seizures and other causes can look similar. A clinician may need the story from you or a witness, a medication review and a physical assessment.

If someone feels faint, help them lie flat and raise their legs if there is no injury or breathing problem. Keep the area clear, check that they are breathing normally, and do not give food or drink while they are unconscious. Once fully alert, they can sit up slowly and sip fluid if safe. Do not drive, climb or bathe alone until the cause is clearer.

Arrange a GP Consultation after any unexplained faint, especially if it happened more than once or followed a new medicine. Write down what happened before, during and after the event, including posture and recovery.

Call emergency services if the person does not wake promptly, is not breathing normally, has chest pain, severe breathlessness, a new severe headache, prolonged confusion, a seizure, significant injury, or fainted during exertion. Urgent assessment is also needed for black stools, heavy bleeding, a very irregular heartbeat or repeated fainting.

Ask whether the episode could be related to posture, medicines, heart rhythm, hydration or blood sugar, and whether you need blood-pressure checks in different positions or further tests. Mention pregnancy, heart history and any family history of sudden cardiac death.