Vasovagal nerve syndrome, or vasovagal reaction, is a reaction of the involuntary nervous system that causes a reduction in blood pressure and dilation of the blood vessels in the legs, leading to loss of consciousness, according to MedicineNet. This reaction is commonly known as a fainting episode.
Potential causes of a vasovagal reaction fainting spell, or vasovagal syncope, include internal and external stresses such as strenuous exercise, panic, fright upon the sight of blood, heat exposure and prolonged standing. The reaction causes a rapid drop in heart rate and blood pressure, which in turn reduces the amount of oxygenated blood flowing through the brain and leads to fainting, notes Healthgrades.
An isolated episode of vasovagal syncope is generally not a serious medical issue, though a person may be at risk of injury if the fainting episode causes her to fall, notes Mayo Clinic. People usually regain consciousness less than one minute after the episode begins, but should remain seated or lying down for at least 15 minutes after fainting to reduce the likelihood of a repeated episode. Vasovagal syncope is sometimes symptomatic of an underlying heart or brain condition. People should consult a doctor to test for these possible causes after experiencing a fainting episode.