Fainting is a loss of consciousness that happens quickly and sometimes without warning. A fainting episode usually resolves within seconds to minutes. If fainting is caused by another condition, then the condition will need to be treated.
In general, fainting is caused by decreased blood flow to the brain.
Blood Flow to the Brain
Decreased blood flow to the brain can be caused by:
Most commonly, vasovagal spells. Vasovagal spells can occur:
- During medical procedures
- During times of high stress, trauma, or fright
- After standing still for a long period of time
- Orthostatic hypotension, low blood pressure when standing
- Hypoglycemia, which is low blood sugar
- Stroke or transient ischemic attack
- Abnormal heart rhythms
- Heart conditions
- Blood loss
Fainting can also occur as a side effect to medications. These include:
- Blood pressure medications
- Medications to regulate heart rhythms
- Certain antidepressants
Factors that increase your risk of fainting include having a history of fainting.
Symptoms may include:
- Sudden loss of consciousness
- Inability to remain standing or sitting
- Consciousness regained without any need for intervention
- Lightheadedness before losing consciousness
When Should I Call My Doctor?
Call your doctor if you are having episodes of fainting. This is especially important if you:
- Have a heart condition
- Have a job where you or others may be at risk if you faint. Examples include airline pilot, bus driver, or machinist.
When Should I Call for Medical Help Immediately?
Call for emergency medical services right away if you have:
- Weakness or numbness of face, arm, or leg, especially on the left side of the body
- Loss of balance, coordination problems
- Vision problems
- Severe headache
- Rapid, irregular heartbeat; chest pain
You will be asked about your symptoms and medical history. A physical exam will be done.
Your bodily fluids may be tested. This can be done with blood tests.
Your heart activity may be tested. This can be done with:
Your brain activity may be tested. This can be done withelectroencephalogram (EEG).
Additional tests may be done. They may include a tilt table test.
If initial tests are unclear, brain images may be taken. This can be done with:
Treatment will depend on the underlying condition that has caused fainting. This may include medications, lifestyle changes, or surgery.
Knowing the warning signs of fainting can help prevent injury. If warning signs are present, the person should be encouraged to sit or lie down right away.
Decreasing the risk of fainting will depend on the cause. Some factors that may help include:
- Rising slowly and carefully from lying down. Start by sitting up for a minute and then stand up.
- Drinking plenty of fluids.
- Discussing helpful dietary changes with your doctor. This may include eating smaller, more frequent meals throughout the day.
- Avoiding alcohol or other drugs.
There are certain physical movements that rapidly increase blood pressure and blood flow to the brain. These movements may prevent fainting after warning signs appear. Examples of physical movements may include:
- Crossing your legs while tensing the muscles of legs, abdomen, and buttocks.
- Forcefully squeezing a rubber ball or other object as hard as possible.
- Gripping one hand with the other while tensing both arms and raising the elbows slightly.
American Heart Association
Family Doctor—American Academy of Family Physicians
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Last reviewed January 2015 by Rimas Lukas, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.