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.

Source: http://www.mayoclinic.com

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.

Source: http://www.mayoclinic.com

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

Source: http://www.mayoclinic.com

The diagnosis of vasovagal syncope often involves ruling out other possible causes of your fainting — particularly heart-related problems. These tests may include:

• Electrocardiogram. This test records the electrical signals your heart produces. It can detect irregular heart rhythms and other cardiac problems that can cause fainting. In some cases, you may need to wear a portable monitor for at least a day or as long as a month.
• Echocardiogram. This test uses ultrasound imaging to view the heart and look for conditions, such as valve problems, that can cause fainting.
• Exercise stress test. This test studies heart rhythms during exercise. It's usually conducted while you walk or jog on a treadmill.
• Blood tests. Your doctor may look for conditions, such as anemia, that can cause or contribute to fainting spells.

Tilt table test

If there appear to be no heart problems causing your fainting, your doctor may suggest you undergo a tilt table test. For a tilt table test:

• You lie flat on your back on a table.
• The table changes position, tilting you upward at various angles.
• A technician monitors your heart rhythms and blood pressure to see if the postural changes affect them.

Source: http://www.mayoclinic.com

Even with treatment, not all vasovagal syncope episodes can be avoided. 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.

Source: http://www.mayoclinic.com