Vasovagal syncope, or fainting due to falling blood pressure and resulting reduction in circulation to the brain, is most common in children and young adults, according to WebMD. Vasovagal syncope is a frequent cause of fainting in general, states Mayo Clinic. Certain factors increase the risk of this type of fainting, including fear, prolonged periods of standing, the sight of blood or having blood drawn, or heat exposure.
The vagus nerve, a cranial nerve, is responsible for the control of heart rate regulation, according to Healthlne. When stimulated, the vagus nerve can trigger a drop in blood pressure and heart rate, leading to fainting. Before vasovagal syncope episodes, patients typically report nausea, blurred or grayed vision, lightheadedness and feeling warm, according to WebMD. Long vasovagal fainting spells can cause seizures, but most fainting spells only last a few minutes.
While fainting is relatively common, accounting for 6 percent of hospital admissions, vasovagal syncope can occur without other medical cause, according to WebMD. Vasovagal syncope happens when someone has a disproportionate physical reaction to a triggering experience, such as serious emotional distress, according to Mayo Clinic. Because blood pools in the legs when someone is standing up, these syncope episodes often occur when a patient is standing. The main risk associated with vasovagal syncope is incidental injury from the fall during fainting, a risk that is particularly pronounced in the elderly, states WebMD.