Fainting occurs when a person suddenly loses consciousness, most often due to a momentary drop in the supply of the blood to the brain. Also known as syncope, it is usually a brief episode that lasts just a couple of minutes and is followed by a rapid, complete recovery.

Mental disorders such as specific phobias, eating disorders, panic disorder and other conditions can sometimes cause a patient to faint. In addition, patients who use certain medications (including antipsychotics and antidepressants) to treat emotional disorders may experience fainting as a side effect of those medications.

During an episode of fainting, the autonomic nervous system (ANS) first creates an exaggerated response by increasing heart rate (rapid beats) and decreasing peripheral circulation (pale color) in an attempt to keep the blood flow stable. Following this initial exaggerated response, the blood pressure drops rapidly, reducing the blood flow to the brain. This inadequate blood flow causes the person to lose consciousness, and often, they will fall to the ground.

Once the person is lying flat, the blood flow to the brain quickly increases because it no longer has to fight gravity. For this reason, the person usually quickly regains consciousness. The patient may still feel tired for anywhere from a few minutes to a few hours before recovering.

In many cases, fainting may not be medically significant and should not worry the patient. However, in other cases, fainting may be caused by a serious underlying medical condition, such as heart rhythm disturbance (arrhythmia) or seizure disorder (e.g., epilepsy). Therefore, any episode of fainting should be considered potentially serious until a medical professional has determined otherwise and the cause is identified. This is particularly true of people who have heart-related problems, high blood pressure or diabetes.