Syncope is a loss of consciousness (fainting) that occurs when blood pressure drops very low and not enough blood reaches the brain. A person may have shortness of breath, palpitations, or chest discomfort before fainting.
The reduction in blood flow usually happens quickly, which causes symptoms to appear suddenly.
Syncope can be caused by several conditions, but it most often occurs when changes in heart rate or heart rhythm reduce the amount of blood flow to the body. Fainting caused by a problem in the heart is called cardiac syncope. Other types of syncope that are not linked with heart problems include neurally mediated syncope, also called vasovagal, neurocardiogenic, and vasodepressor syncope.