Syncope

Syncope is the medical term for fainting or blacking out. It is a sudden loss of consciousness, usually for a short time. It is mostly because there is not enough oxygen in the brain. It can be for other reasons. 
Fainting is quite common. It usually happens in two age ranges: the teenage years, and during older age. The chance of a person fainting at least once in a lifetime is about 40 to 50 percent. Syncope causes 1 to 3 percent of all attendances to emergency departments and 1 to 6 percent of all hospital admissions.