This is what happened to me and why I ended up staying in the hospital. It's quite frightening as you loose all control of everything.
Definition of Vasovagal reaction
Vasovagal reaction: A reflex of the involuntary nervous system that causes the heart to slow down (bradycardia) and that, at the same time, affects the nerves to the blood vessels in the legs permitting those vessels to dilate (widen). As a result the heart puts out less blood, the blood pressure drops, and what blood is circulating tends to go into the legs rather than to the head. The brain is deprived of oxygen and the fainting episode occurs. The vasovagal reaction is also called a vasovagal attack. The resultant fainting is synonymous with situational syncope, vasovagal syncope, vasodepressor syncope, and Gower syndrome which is named for Sir William Richard Gower (1845-1915), a famous English neurologist. See also: Syncope.