Fainting: Causes & Prevention


Jody fainted while giving blood at a blood drive. Gerald passed out in the aisle on his way out of the movie theater.

If you have ever fainted, or nearly fainted, the event probably caused you a great deal of embarrassment and consternation, even if you never reported it to your doctor. In fact, fainting is fairly common; about 40 percent of Americans have fainted at least once. And, in most cases, it is not associated with any major medical concern.

Known medically as syncope or transient loss of consciousness, fainting is caused by a brief episode of impaired blood flow to the brain. By definition, it is not a concussion, stroke or seizure–all of which may involve loss of consciousness but can have much more severe consequences.

When you faint, you black out only briefly, then return to normal consciousness. Should you hit your head during the fall, you may, however, have a concussion as a result. In either case, it’s a good idea to see your doctor and find out what caused the episode.

Fainting can be associated with potentially serious heart problems; usually, it is not. A physical examination, some questioning and, perhaps, an electrocardiogram will help the doctor decide whether you need reassurance or some further testing.

The vast majority of fainting episodes are congregated in two age groups: 1) adolescents and 2) adults age 65 and over. In each group, there are numerous possible causes, but most have to do with:

  •  a change in the heart’s pumping action,
  •  reduced pressure in blood vessels or
  •  low levels of blood and fluid in the arteries.
Some individuals get a warning ahead of time–lightheadedness, sweating and weakness–particularly in the legs. If you learn to recognize these signs and act fast enough, you may be able to avoid the actual syncope by sitting or lying down.

Once the fall occurs, blood pressure rises, and the person regains control quickly. This is what distinguishes syncope from more serious reasons for loss of consciousness, such as a seizure, stroke or concussion.

Nerve-Related Causes

Jody, 17, suffered from what is known as vasovagal syncope. Very common among teenagers, vasovagal fainting occurs in stressful, frightening, embarrassing or uneasy situations. These may include blood draws, coughing, urination or defecation.

Again, the culprit is low blood pressure in the vessels leading to the brain, but the change occurs as a result of action by the vagus nerve, which controls the release of the neurochemicals adrenaline and acetylcholine. When too much acetylcholine is released, the heart rate slows and blood vessels dilate, making it more difficult for the heart to combat gravity in pumping blood to the brain.

Young females who “swoon” in 18th and 19th century novels suffer from vasovagal syncope. Some swoon when they hear bad news; others, when they see blood or a gory scene. These women are also highly likely to be squeezed into tight corsets, resulting in compression of nerves and blood vessels, another reason for syncope. Pregnant women are also at risk of this type of fainting, particularly if they have been standing for an extended period, allowing blood to pool in their legs.

The most common reason for fainting among youth, vasovagal syncope ordinarily does not require medical intervention, only some care in avoiding situations that might trigger a collapse.

Diagnosis of a young person who has fainted has to include a suspicion of heart problems, however, and perhaps a few tests.

Some youth–most notably athletes–have an abnormal thickening of parts of the heart muscle, a condition known as cardiomyopathy. When the heart is asked to beat harder during competition, this thickened area may obstruct blood as it tries to leave the heart. This is a frequent cause of sudden death in high-level athletes.

Heart-Related Causes

Gerald, 72, had been sitting in the theater for nearly two hours, and his blood pressure dropped when he stood up suddenly. That’s a very common problem among seniors known as postural or orthostatic hypotension. The solution, he learned, is to stand up more slowly, giving his blood pressure time to adjust before starting to walk.

Gerald was at risk of postural hypotension for several reasons. He was taking a prescription diuretic that reduced his blood volume. In addition, this diuretic increased the risk of imbalances among electrolytes such as sodium, potassium, magnesium and bicarbonate. He was also taking a beta blocker, a drug that slows the heart beat.

Other medications that can contribute to decreased blood flow to the brain include calcium channel blockers, antidepressants and pain killers.

good for his heart but puts him at risk of dehydration if he neglects to drink enough water. Young athletes also face this problem, particularly in hot weather, and it is another risk factor for syncope.

Finally, his episodes of lightheadedness eventually led to a diagnosis of atrial fibrillation, an arrhythmia of the upper chambers of the heart. This causes the heart to beat erratically and faster or slower than normal, sometimes reducing blood flow to the brain.

Structural and valve problems and damage to the heart such as that caused by a heart attack can also cause episodes of fainting. These causes are relatively rare, however.

As with vasovagal syncope, persons with heart-related symptoms can usually learn to manage them. Waiting just a few minutes after rising from a sitting or lying position can help prevent postural hypotension. You can also flex the muscles in your arms, legs and abdomen to get an increase in blood pressure. Persons taking medications should be particularly careful about drinking plenty of fluids. And if some medications are persistently troublesome, there are alternative drugs that can be prescribed.

Most fainting is benign, although the risk of suddenly falling has dangers, particularly for a frail, elderly person. Even one episode is not something to ignore or deny; see your doctor to get diagnosis and treatment.

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