Vasovagal syncope (fainting)

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Definition

Syncope (commonly referred to as fainting) is a loss of consciousness that occurs when you experience a significant reduction of blood flow to your brain. Fainting is often caused by a significant drop in blood pressure or from a very slow heart rate. The result is a sudden reduction of blood flow to your brain, causing you to lose consciousness.

The most common cause of fainting is due to vasovagal syncope. Vasovagal syncope is triggered by a stimulus that results in an exaggerated and inappropriate response in the part of your nervous system that regulates involuntary body functions, including heart rate and blood flow (autonomic nervous system). When some sort of stimulus triggers this exaggerated response, both your heart rate and blood pressure drop, quickly reducing blood flow to your brain and leading to loss of consciousness. A person who has fainted due to vasovagal syncope recovers quickly, usually within seconds or a few minutes.

Common triggers of vasovagal syncope include standing for long periods, dehydration, the sight of blood, coughing, urination, having a bowel movement and emotional distress. But in some cases, the cause of vasovagal syncope can't be determined.

Fainting is common, and treatment is unnecessary in most cases. However, sometimes fainting can indicate an underlying disease for which you'll need treatment.

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