Vasovagal syncope (vay-zo-VAY-gul SING-cuh-pee) is the most common cause of fainting. Vasovagal syncope occurs when your body overreacts to triggers, such as the sight of blood or extreme emotional distress. The trigger results in vasovagal syncope — a brief loss of consciousness caused by a sudden drop in your heart rate and blood pressure, which reduces blood flow to your brain.
Vasovagal syncope is usually harmless and requires no treatment. However, you can 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.