Syncope or fainting is your bodies mechanism to make you lie down to get more blood supply to the brain. It occurs when there is not enough blood supply to the brain. The most common cause is vasovagal syncope, which has a good prognosis. More worrisome causes are heart valve problems, such as aortic stenosis, heart attacks, abnormal heart rhythms, and problems in the brain. Video courtesy of eMedTV.com