Fainting (syncope)

Fainting (syncope) is a sudden, brief loss of consciousness caused by a temporary reduction in blood flow to the brain, followed by a rapid and complete recovery. The great majority is a simple faint (vasovagal syncope): a normal reflex triggered by standing for a long time, heat, pain, fear, the sight of blood, or straining, in which the heart rate and blood pressure briefly drop. There is usually a warning — light-headedness, nausea, sweating, blurring or ringing in the ears — and it comes on when upright and recovers quickly on lying down. A second common type is orthostatic (from standing up), where blood pools in the legs; this is more likely with dehydration, blood loss or anaemia, and some medicines. The important minority to identify is cardiac syncope, from a heart-rhythm disturbance or a structural heart problem, which can be dangerous. Features that raise concern for a heart cause are: fainting during exertion, fainting with no warning at all, fainting while lying down, palpitations just before, and a family history of sudden death.

• Simple faint (vasovagal) — the commonest; triggered by standing, heat, pain, fear, or straining, with warning symptoms.
• Orthostatic (on standing up) — dehydration, blood loss, anaemia, or blood-pressure medicines.
• Anaemia — makes fainting more likely.
• Low blood sugar — in people with diabetes on treatment.
• Cardiac (heart-rhythm or structural) syncope — the important dangerous type, especially with the warning features below.
• Situational — coughing, passing urine, swallowing.
• Medications and alcohol.

The cause of fainting is worked out mainly from the story — what happened before, during and after — plus an examination, a lying/standing blood pressure, and an ECG (heart tracing), which is done in essentially everyone to look for a heart-rhythm clue. Blood tests support this: a full blood count and ferritin for anaemia, glucose for a low-sugar cause, and electrolytes and kidney function for dehydration. Further heart tests (heart monitoring, an echocardiogram) are arranged when a cardiac cause is suspected. Mediora.AI can surface an anaemia, glucose or electrolyte pattern that contributes, but the key to fainting is the clinical assessment and ECG, not blood tests alone.