Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. For regularly updated information on a variety of health topics, please visit familydoctor.org, the AAFP patient education website.

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Am Fam Physician. 2017;95(5):online

See related article on syncope

What is fainting?

Fainting, also called syncope (SIN-koh-pee), happens when your brain doesn't get enough oxygen. You pass out for a short time, then wake up.

What causes it?

Fainting can be caused by many things. Reflex syncope is when something happens to trigger the fainting, such as going to the bathroom or being upset by something, such as seeing blood.

Orthostatic hypotension syncope happens when your blood pressure gets too low to get enough blood to your brain. This can happen from standing up too quickly, not drinking enough water, or losing a lot of blood. Taking certain medicines can also cause it.

Cardiac syncope happens when your heart doesn't pump enough blood to the brain. This can be because your heart doesn't beat properly, or because your heart isn't shaped normally.

How is it diagnosed?

Your doctor will ask you questions, examine you, and test your heart with an EKG to find out why you fainted. These things are usually enough to find the cause, but if they're not, you may need more tests, such as blood tests, a heart ultrasound, or heart monitoring. Your doctor will also find out if you're at risk of more severe problems, and will decide if you need to be admitted to the hospital.

How is it treated?

It depends on the cause. For reflex syncope, you might just need to avoid whatever triggered the fainting. For orthostatic hypotension syncope, you need to be careful when standing up, and you might need to stop taking medicines that could be causing the problem. For cardiac syncope, you might need medicine, a procedure, or a device put inside your chest to treat an abnormal heartbeat.

Where can I get more information?

Your doctor

AAFP's Patient Information Resource

National Institute of Neurological Disorders and Stroke

National Library of Medicine

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