Why People Faint

February 1, 2013
Bottom Line Health
Satish R. Raj, MD

Fainting is a frightening experience—especially when you don’t know the cause.

What you may not realize: Up to half of all Americans will faint at least once during their lives.

The cause is often relatively harmless, such as standing up too quickly, getting overheated, becoming dehydrated, receiving bad news or experiencing intense fear. You can even faint when a vigorous cough stimulates nerves that trigger a decrease in blood pressure and brain circulation. But in some cases, fainting can be a red flag for a potentially serious medical condition that affects your heart, lungs or nervous system.


If you’ve fainted for the first time (and have no idea what could have caused it), play it safe and contact your doctor to find out whether you need to be examined. But people who suddenly experience more than one fainting episode in a short period of time—especially those who have been diagnosed with another health problem—should definitely see their doctors. A long history of fainting spells makes it less likely that the cause is serious.

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More serious causes…

Heart disease. Structural heart problems, such as cardiomyopathy (a weakened heart) or heart-valve conditions, can cause fainting spells. An abnormal heart rhythm, which may increase risk for cardiac arrest or a heart attack, can lead to fainting, too.

Important: If you faint and have a first-degree relative (parent, sibling or child) who has suffered an unexplained sudden cardiac death, you may need to be examined by a heart-rhythm specialist (cardiac electrophysiologist).

Pulmonary embolism. This condition involves blood clots in an artery that can reduce blood flow to the lungs. Italian researchers found in a recent study that 10% of patients with an embolism reported fainting as an initial symptom.

Medication side effects. Patients who take medications for high blood pressure, including diuretics (water pills), will sometimes have excessive drops in blood pressure when they stand up. This is not likely to cause fainting in younger patients, but the body’s ability to regulate blood pressure declines with age.

Tamsulosin (Flomax), often prescribed for an enlarged prostate gland, also can trigger prefainting sensations.


The cause of fainting can be tricky to diagnose. Initial tests might include a complete blood count (to check for anemia), kidney-function tests and/or tests for glucose.

If your doctor suspects that your fainting is due to a cardiovascular problem, he/she might advise that you wear a heart monitor to detect problems with heart rates or rhythms.


If you know that you are susceptible to fainting (and you have discussed this with your doctor), it’s usually easy to prevent future episodes.

Main steps…

Stand up slowly. This is one of the most effective ways to prevent a common cause of fainting. Example: When you get out of bed, first rise to a sitting position…wait about 20 seconds for your blood pressure to stabilize…then stand up. You might want to hold on to the back of a chair or a dresser for about 40 seconds once you’re on your feet. This will keep you from falling if you get light-headed.

Drink more fluids. Many people have their first (and only) fainting episode on hot summer days. You can have low blood volume when you are hot and perspiring. This makes it harder for the body to regulate blood pressure and blood flow to the brain.

Drink about six to eight eight-ounce glasses of water during the day—add an extra glass or two when it’s hot and you’re exerting yourself more than usual.

Get enough salt. Low salt intake, combined with exertion or not drinking enough water, can lead to low blood volume that may trigger dizziness and fainting.

As long as your doctor hasn’t prescribed a low-salt diet, it might be helpful to have a daily serving or two of salt-containing foods, such as crackers, pretzels or sports drinks. If you are on a low-salt diet, talk to your doctor.

Lie down to avoid falls. Fainting is the cause of about 20% of fall-related injuries in older adults. Fortunately, most fainting spells are preceded by prefainting symptoms such as dizziness, light-headedness and/or cold, clammy sweating. If you notice these symptoms and lie down immediately, you can often short-circuit the episode. If you happen to be in a location where you can’t lie down, at least sit down on the ground or squat to prevent a fall.

New thinking: Doctors used to advise patients to put their heads between their legs if they felt a fainting spell coming on. However, now lying down is recommended.

More help: One study found that exercises such as the following can help halt a fainting episode—crossing your legs at the ankles while squeezing your thighs together and tensing your abdominal and buttocks muscles…or interlocking your fingertips in front of your chest and pulling your arms in opposite directions.

Review medications with your doctor. If you’ve had a fainting episode, ask your doctor if it could be a medication side effect.


When you see someone lose consciousness and collapse, you won’t know at first if the person is injured, still breathing or even alive.

Someone who faints will recover spontaneously (typically in less than a minute). This is usually not an emergency.

However: Unless you’re a health professional, you won’t know what’s going on. The person could have fainted or experienced something far worse, such as a heart attack. Don’t take any chances.

If someone loses consciousness…

Place the person on his/her back. Check the ABCs—airway, breathing and circulation. If the person isn’t breathing , call 911 and begin chest compressions.

Allow the person to lie on the ground. This increases circulation to the brain. Loosen his collar, belt or other restrictive clothing. When it’s time to help him stand up, do it slowly.

Call 911 if the person does not regain consciousness within a minute.