Learn about what causes a brief loss of consciousness and when to see a doctor if this happens to you.
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 that 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:
During a vasovagal syncope episode, bystanders may notice:
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.
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've 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:
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.
Diagnosing vasovagal syncope often begins with a physical examination. During the physical exam, your doctor will listen to your heart and take your blood pressure. He or she may also massage the main arteries in your neck to see if that causes you to feel faint.
Your doctor may also recommend several tests to rule out other possible causes of your fainting — particularly heart-related problems. These tests may include:
In most cases of vasovagal syncope, treatment is unnecessary. Your doctor may help you identify your fainting triggers and discuss ways you might avoid them.
However, if you experience vasovagal syncope often enough to interfere with your quality of life, your doctor may suggest trying one or more of the following remedies:
It's a good idea to prepare for your appointment to make the most of your time with your doctor.
Questions your doctor might ask you include: