Vasovagal syncope (vay-zoh-VAY-gul SING-kuh-pee) occurs when you faint because your body overreacts to certain triggers, such as the sight of blood or extreme emotional distress. It may also be called neurocardiogenic syncope.
The vasovagal syncope trigger causes your heart rate and blood pressure to drop suddenly. That leads to reduced blood flow to your brain, causing you to briefly lose consciousness.
Vasovagal syncope is usually harmless and requires no treatment. But it's possible you may injure yourself during a vasovagal syncope episode. Your doctor may recommend tests to rule out more serious causes of fainting, such as heart disorders.
Before you faint due to vasovagal syncope, you may experience some of the following:
- Pale skin
- Tunnel vision — your field of vision narrows so that you see only what's in front of you
- Feeling warm
- A cold, clammy sweat
- Blurred vision
During a vasovagal syncope episode, bystanders may notice:
- Jerky, abnormal movements
- A slow, weak pulse
- Dilated pupils
Recovery after a vasovagal episode generally begins in less than a minute. However, if you stand up too soon after fainting — within about 15 to 30 minutes — you're at risk of fainting again.
When to see a doctor
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.
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 (dilate.) This allows blood to pool in your legs, which lowers your blood pressure. Combined, the drop in blood pressure and slowed heart rate quickly reduce blood flow to your brain, and you faint.
Sometimes there is no classical vasovagal syncope trigger, but common triggers include:
- Standing for long periods of time
- Heat exposure
- Seeing blood
- Having blood drawn
- Fear of bodily injury
- Straining, such as to have a bowel movement
You may not always be able to avoid a vasovagal syncope episode. If you feel like you might faint, lie down and lift your legs.
This allows gravity to keep blood flowing to your brain. If you can't lie down, sit down and put your head between your knees until you feel better.