Fainting (also known as syncope) is a sudden and brief loss of consciousness. In some cases, the person both faints and falls to the ground (passes out). Fainting occurs when there is a decrease in the amount of oxygen or blood flow to the brain. 

Many different stimuli can cause fainting, including neurological problems such as brain tumors or bleeding into the brain. In addition, conditions such as Parkinson's disease or a history of strokes can increase a person’s vulnerability to fainting.

Just before people faint, their skin tone may turn pale and their muscle tone may relax. They may feel weak or nauseated, and have a sensation that surrounding noises are fading into the background. After fainting, people usually regain consciousness within a couple of minutes and quickly make a complete recovery.  

In many cases, fainting is a medically harmless condition that should not worry the patient. However, other types of fainting may be caused by a serious underlying medical condition. For this reason, all episodes of fainting should be viewed as potentially serious until a physician has had a chance to examine the patient and diagnose the cause of these episodes.

Fainting is sometimes related to malfunctions in the body’s autonomic nervous system, which controls breathing and heart rate. Other neurological conditions may also affect parts of the brain or nervous system and produce fainting spells. Physicians investigating patients who faint may consider many conditions when searching for a source. Tests that record the function of the heart and brain may provide insight into the causes of fainting. However, in some cases the cause of fainting cannot be identified.