Harvard Health Question: What Happens When You Faint?

Fainting, the temporary loss of consciousness that doctors call syncope (SINK-uh-pee), can be embarrassing, scary, and dangerous. It’s also quite common — an estimated one in three people faints at least once in their lifetime. People pass out when the brain doesn’t get enough blood and becomes deprived of fuel and oxygen. This is usually caused by a sudden drop in blood pressure (hypotension).

How Serious Is It?

The most common type of fainting — what doctors call “uncomplicated” syncope — is often preceded by breaking out in a sweat or feeling dizzy. Standing up for a long time can cause blood to languish in the legs, making less available to the brain. Sitting up or standing quickly after lying down can also cause a faint.

Extreme emotion or pain can cause the heart to slow down at the same time blood vessels open wide. This combination makes blood pressure plummet — and down you may go. This is what happens when some people see a hypodermic needle or blood.

When a heart abnormality is involved in fainting, things get a bit more complicated. About 15 percent of fainting episodes are related to heart rhythm problems, including the abnormally slow heartbeat known as bradycardia. Blockages in arteries supplying the heart and heart muscle malfunctions can also temporarily disrupt the flow of blood to the brain and cause fainting. Interestingly, people don’t usually faint when they’re having a heart attack.

If you feel faint from prolonged standing, cross your legs and tense the muscles in your lower body. The resulting blood pressure boost may stave off the faint or at least give you time to get to a safe place.

After a Faint

Fainting often involves falling, which can lead to injury, so it’s a good idea to get checked out by a doctor if you’ve fainted. If you have heart disease, a faint definitely warrants a prompt medical visit.

Updated diagnostic guidelines say that anyone who has fainted should see a doctor for a physical examination and medical history (Annals of Internal Medicine). It helps if someone who witnessed the faint reports what he or she saw. A medication review could uncover additional clues — many drugs can lead to hypotension and fainting. Even if all signs point to uncomplicated fainting, the guidelines recommend an electrocardiogram (ECG) to rule out the possibility of irregular heartbeats.

If anything about the exam leads the doctor to suspect a cardiac cause, he or she may refer you to an electrophysiologist to get more information about your heart’s electrical activity or to a general cardiologist to investigate the possibility of some other heart malfunction.

According to the updated guidelines, frequent fainters should be assessed with a wearable Holter monitor, which takes continuous ECG readings, for 24 to 48 hours. For those who faint less often, an external event recorder or implanted recorder is most likely to spot a heart rhythm problem.

Coping With Fainting

If you are an uncomplicated fainter, try to avoid the situations that trigger your faints. If medical procedures are triggers, let your provider know so precautions can be taken. If you feel faint, try to lie down somewhere safe and elevate your feet.

If a heart-specific cause of fainting is found, treatment options might include medications to control abnormal heart rhythms, a pacemaker if your fainting is caused by an abnormally slow heartbeat, or an implantable cardioverter-defibrillator if a more serious rhythm problem exists.

– Harvard Heart Letter


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