Vasovagal Response or Syncope is; When you pass out or faint for no apparent reason.

Vasovagal Response; Syncope What is it and what causes it? It's cause by a response to a stimuli. The event happens, the vascular system either restricts the blood vessels or lets them relax so more blood can flow through the body. This can cause a drop in blood pressure and then the person can faint. It can happen fast and sometimes with no warning. The main danger with this is the patient can hit their head.