Overview

Syncope, commonly called fainting, is a brief, usually reversible loss of consciousness caused by transient global cerebral hypoperfusion. The word derives from Greek synkopē, meaning "a cutting off." Most episodes are short-lived and self-limited, but syncope can also be a sign of potentially life-threatening heart disease. For a concise technical definition see the medical term.

Typical features and mechanisms

Before fainting people often report lightheadedness, sweating, nausea, visual changes (tunnel vision), or ringing in the ears. Recovery is typically rapid when the person lies horizontal. The underlying problem is inadequate oxygen delivery to the brain, usually from a fall in systemic blood pressure. For a plain explanation of loss of consciousness, consult this resource.

Common causes

  • Vasovagal (neurocardiogenic) syncope: reflex-mediated vasodilation and slowing of the heart rate, often triggered by pain, emotional stress, or prolonged standing.
  • Orthostatic hypotension: a drop in blood pressure on standing due to dehydration, medications, or autonomic failure.
  • Cardiac syncope: arrhythmias or structural heart disease that abruptly reduce cardiac output.
  • Less commonly, metabolic problems such as severe hypoglycemia or pulmonary causes may contribute.

For differences among these types, see further reading.

Evaluation and diagnosis

Assessment begins with a careful history and physical exam focusing on the circumstances of the event, preceding symptoms, medication review, and family history of sudden death. Basic tests include orthostatic vital signs and a 12-lead electrocardiogram. More specialized tests—ambulatory ECG monitoring, tilt-table testing, or echocardiography—are used when the cause remains unclear or cardiac syncope is suspected. Practical guidance can be found at clinical resources.

Management, prevention, and when to worry

Immediate care involves laying the person flat and elevating their legs to restore cerebral blood flow. Long-term treatment targets the underlying cause: stopping or changing precipitous medications, increasing fluids and salt for orthostatic problems, using compression stockings, or treating cardiac disease. Red flags that warrant urgent cardiac evaluation include syncope during exertion, occurrence while supine, associated chest pain or palpitations, or a family history of sudden cardiac death.

Importance and prognosis

Syncope is common—many people faint at least once in life—and most episodes are benign. However, identifying the minority with cardiac causes is crucial because those cases carry higher risk. Appropriate evaluation balances avoiding unnecessary tests with timely detection of serious conditions.