Vasovagal syncope, the medical term for fainting due to suppression of the functions of the vagus nerve, occurs when this essential part of the nervous system that controls the heart rate and blood pressure malfunctions, says Mayo Clinic. An external trigger typically causes this malfunction.
When the heart rate drops, the blood vessels in the legs widen, and blood pools there, causing the blood pressure to drop, according to Mayo Clinic. The drop in blood pressure leads to the fainting episode. Some common triggers for vasovagal syncope include the sight of blood, standing for long periods of time and fear of bodily harm.