Blackouts and dizzy spells are very common symptoms in the general population. The medical term for reversible brief loss of consciousness (a simple faint) is syncope. Although syncope is most often not due to serious heart problems, it is an important event and always warrants careful evaluation. Presyncope describes a feeling of lightheadedness as though one might blackout, but consciousness is preserved.
The most common cause of both syncope and presyncope is a sudden fall in blood pressure. Sometimes there is an obvious precipitating factor (e.g. having a blood test or the sight of blood) but at other times it seems a random event. Most times, loss of consciousness is preceded by typical symptoms such as a feeling of warmth, light headedness, dimming of vision, and nausea and the person may feel sweaty or clammy and look very pale. Recovery is usually prompt, but sometimes the blood pressure remains persistently low for 15-30 minutes with associated “grogginess” and people often feel “washed out” the next day.
Less commonly, but importantly, syncope and presyncope may be caused by heart rhythm abnormalities, such as a pause in the heart beat or racing of the heart. These problems may be solely due to problems with the heart’s electrical system or associated with disease of the heart muscle or valves. Usually the correct diagnosis will be apparent from conducting a careful history and heart examination and checking the electrocardiograph. Problems with a slow heart rate are often treated with an artificial pacemaker.