Fainting (Syncope): Get the Facts on Causes

Syncope - is the medical term for fainting or passing out. It is caused by a temporary drop in the amount of blood that flows to the brain.

Vasovagal syncope (vay-zoh-VAY-gul SING-kuh-pee) is one of the most common causes of fainting. Vasovagal syncope occurs when your body overreacts to certain triggers, such as the sight of blood or extreme emotional distress.

The vasovagal syncope trigger causes a sudden drop in your heart rate and blood pressure. That leads to reduced blood flow to your brain, which results in a brief loss of consciousness.

Vasovagal syncope is usually harmless and requires no treatment. But it's possible you may injure yourself during a vasovagal syncope episode. Also, your doctor may recommend tests to rule out more-serious causes of fainting, such as heart disorders.

Symptoms

Before you faint due to vasovagal syncope, you may experience some of the following:

Skin paleness
Lightheadedness
Tunnel vision — your field of vision is constricted so that you see only what's in front of you
Nausea
Feeling of warmth
A cold, clammy sweat
Yawning
Blurred vision

During a vasovagal syncope episode, bystanders may notice:

Jerky, abnormal movements
A slow, weak pulse
Dilated pupils

Recovery after a vasovagal episode begins soon after fainting, generally in less than a minute. However, if you stand up too soon after fainting — within 15 to 30 minutes or so — you're at risk of fainting again.

When to see a doctor

Because fainting can be a sign of a more serious condition, such as a heart or brain disorder, you may want to consult your doctor after a fainting spell, especially if you never had one before.

Causes

Vasovagal syncope occurs when the part of your nervous system that regulates heart rate and blood pressure malfunctions in response to a trigger, such as the sight of blood. Your heart rate slows, and the blood vessels in your legs widen. This allows blood to pool in your legs, which lowers your blood pressure. This drop in blood pressure and slowed heart rate quickly diminish blood flow to your brain, and you faint.

Common triggers for vasovagal syncope include:

Standing for long periods of time
Heat exposure
The sight of blood
Having blood drawn
Fear of bodily injury
Straining, such as to have a bowel movement

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