Condition Basics

What is fainting?

Fainting is a sudden, brief loss of consciousness. When people faint, or pass out, they usually fall down. After they are lying down, most people will recover quickly.

The term doctors use for fainting is syncope (say "SING-kuh-pee").

Fainting one time is usually nothing to worry about. But it is a good idea to see your doctor, because fainting could have a serious cause.

What causes it?

Fainting is caused by a drop in blood flow to the brain. After you lose consciousness and fall or lie down, more blood can flow to your brain so you wake up again.

Most causes of fainting are usually not signs of a more serious illness. In these cases, you faint because of:

• The vasovagal reflex, which causes the heart rate to slow and the blood vessels to widen, or dilate. As a result, blood pools in the lower body and less blood goes to the brain. This reflex can be triggered by many things, including stress, pain, fear, coughing, holding your breath, and urinating.
• Orthostatic hypotension, or a sudden drop in blood pressure when you change position. This can happen if you stand up too fast, get dehydrated, or take certain medicines, such as ones for high blood pressure.

Fainting caused by the vasovagal reflex is often easy to predict. It happens to some people every time they have to get a shot or they see blood. Some people know they are going to faint because they have symptoms beforehand, such as feeling weak, nauseated, hot, or dizzy. After they wake up, they may feel confused, dizzy, or ill for a while.

Some causes of fainting can be serious. These include:

• Heart or blood vessel problems such as a blood clot in the lungs, an abnormal heartbeat, a heart valve problem, or heart disease.
• Nervous system problems such as seizure, stroke, or TIA.

Sometimes the cause is unknown.

How is it diagnosed?

To find the cause of fainting, a doctor will do a physical examination and ask questions about the fainting episode.

The doctor may want to do tests. These tests may include:

• Blood tests.
• Heart tests such as ECG, ambulatory monitoring (with a Holter monitor or event monitor, for example), echocardiogram, or an exercise stress test.
• A tilt table test. This test checks how your body responds to changes in position.
• Tests for nervous system problems, such as CT scan of the head, MRI of the brain, or EEG.

How can you care for yourself?

If you know you tend to faint at certain times (such as when you get a shot or have blood drawn), it may help to:

• Sit with your head between your knees or lie down if you feel faint or have warning signs such as feeling dizzy, weak, warm, or sick to your stomach.
• Drink plenty of fluids so you don't get dehydrated.
• Stand up slowly.

You may need to see a doctor if you have ongoing dizziness or fainting. Ask your doctor when it is safe to drive.