What causes fainting?
Fainting (syncope) can be caused by any condition causing a reduction of circulating blood flow to the brain. The cause of fainting should be evaluated by a health care provider. Fainting occurs when the blood supply to the brain is not enough for its functioning. This may happen in any condition when the heart is not be able to pump enough blood to the brain as in
case of heart valve problems; and if the heart rate is either too slow or too fast, it may also happen if the person is fasting for too long resulting in fall in his blood sugar level or in a diabetic patient.
Light-headedness can accompany mild illness such as the flu or the common cold, and may be a symptom of anxiety. Light-headedness without other symptoms is usually not serious. Actual fainting can be caused by any condition restricting blood flow to the brain; this can be positional, physiological (an automatic body response to a stimulus), or a result of drugs or activity. The more common causes include rigid standing at attention, arising quickly from a prone position, pressure on the neck (tight collar), abnormal heart rate or rhythm, low blood pressure (hypotension), severe pain, injury or fright, alcohol or drugs including anxiolytics, antihistamines, antihypertensives, vasodilators, decongestants, central nervous system depressants, strenuous coughing, straining during a bowel movement or any other Valsalva maneuver (forced exhalation with closure of mouth and nose), and hyperventilation.
The risks of fainting increase with stress; heart disease; some drugs (digitalis, beta-adrenergic blockers); hot humid weather; elderly; and diabetes mellitus. Naturally, preventive measures would be avoidance of the above listed causes. Possible complications could be injuries while fainting, or mistaking cardiac arrest for fainting.