Fainting, or syncope, is a condition in which a person briefly loses consciousness without having a convulsion or head injury. It is distinguished from coma in that it is brief, usually lasting only a few seconds or minutes, and that its cause is not a major disturbance in the functioning of the central nervous system, as is the case in comatose patients,
Faintness is the feeling of being faint and is often described by the patient as dizziness. It is sometimes confused with vertigo, which is characterized by a sensation of spinning or imbalance, as is normally experienced when one whirls around very fast and then stops. In true faintness, the person gets a lightheaded feeling followed by an awareness that he will lose consciousness if he does not lie down. He then faints, and when he regains consciousness there is often a brief period of confusion with respect to where he is and what he is doing. If he does lie down fainting will usually not occur.
Many different conditions may cause fainting, but they all have one thing in common: they decrease temporarily the flow of blood to the brain. The most common cause of fainting is a reflex response in which the blood vessels dilate (widen), so that blood pools in the lower part of the body and less blood is pumped to the brain. Such a reflex response may be stimulated by psychological stress, exposure to heat, a sudden change in position from sitting or lying down to standing, or other factors. Certain drugs used in the treatment of high blood pressure increase this tendency.
Fainting can also be caused by heart disorders that decrease the heart's output. This is particularly common when the valve leading from the heart to the aorta is narrowed (aortic stenosis). Fainting can also occur when there is a disease of the blood vessels leading to the brain. Anemia, in which there is a decreased capacity of the blood to carry oxygen, may cause faintness.
In most instances fainting is not a serious disorder and does not require treatment. However, if a person suffers repeated fainting spells, he should be examined by a doctor to determine if the fainting is due to an underlying disease.