What should you know about neurogenic syncope?

A temporary fall in blood flow to the brain can cause someone to become unresponsive and collapse, followed by recovery. Warning signs may include warmth, nausea, sweating, visual dimming or weakness. A person can faint for several reasons, including dehydration, low blood sugar, anaemia or a heart-rhythm problem such as atrial fibrillation.

A clinician will ask what happened before, during and after the event, examine you and review medicines and medical history. The account from a witness can be especially useful. Fainting with exertion, without warning or with palpitations deserves careful assessment.

If warning symptoms start, lie flat and raise your legs if possible. Loosen tight clothing and move away from hazards. After a collapse, check breathing, keep the person lying down and do not give food or drink until they are fully alert. Arrange medical review after an unexplained episode, even if recovery is quick.

Call emergency services if the person is not breathing normally, does not regain consciousness promptly, has chest pain, severe breathlessness, a severe headache, new weakness, trouble speaking, a significant injury or a seizure-like episode. Urgent assessment is also needed for fainting during exercise or while lying down.

What features of my episode suggest syncope rather than another event? Should I have an ECG or blood tests? Could dehydration, anaemia, low glucose or an irregular rhythm be involved? When can I safely drive or return to exercise?