Fainting after seeing blood is called vasovagal syncope in medical language. When a person sees blood, injury or any sudden stressful situation, the body’s nervous system becomes excessively active. Due to this the heart beat slows down, blood vessels dilate and blood pressure falls. The result of all this is that not enough blood reaches the brain, and the person may feel dizzy and faint. This is more an automatic reaction of the body than fear.

Our brain depends on the constant supply of oxygen and blood. When due to some reason this supply reduces for a few moments, the body starts giving signals, such as feeling lightheaded, darkness before the eyes, nausea, weakness. If proper steps are not taken at that time, the person may become completely unconscious. The body tries to bring the person to the ground so that the brain can get blood again.