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  • Cynthia M. Johnson, MA
Publication Type:





Fainting is a loss of consciousness that happens quickly and sometimes without warning. A person is often alert again in a short amount of time.


Fainting happens when there is a decrease in blood flow to the brain. There are many health problems that can cause fainting.

Some things that can trigger fainting are:

  • Extreme heat
  • Dehydration
  • Long periods of standing
  • Stress, trauma, or fright
Blood Flow to the Brain.

Nucleus factsheet imagehttp://services.epnet.com/getimage.aspx?imageiid=50725072exh38335a_ma.jpgexh38335a_ma.jpgNULLjpgNucleus factsheet imageNULL\\filer01a\Intellect\images\exh38335a_ma.jpgNULL19NULL2004-05-053003805072_11871Copyright © Nucleus Medical Media, Inc.

These health problems may also cause fainting:

Risk Factors

Things that may raise the risk of fainting are:

  • Taking medicine that lowers blood pressure
  • Alcohol use
  • Blood loss
  • Fluid loss, such as from diarrhea or vomiting
  • Not drinking enough fluids
  • Lung disease
  • Environmental factors, such as extreme heat


Fainting is a sudden loss of consciousness that resolves in a short amount of time. Before this happens, a person may feel:

  • Lightheaded
  • Weak
  • Nauseated
  • Sweaty


The doctor will ask about symptoms and health history. The doctor may also ask what was going on right before the fainting occurred. A physical exam will be done. This is often enough to make the diagnosis, though more tests may need to be done. The tests that are done depend on what the doctor believes may be the cause.


If there is an underlying cause, it will need to be treated. Treatment may not be needed for a person who only fainted once.


Some underlying health problems cause people to faint. They will need to be treated.

People who feel as though they may faint can lower the risk with movements that promote blood flow to the brain, such as:

  • Crossing their legs while tensing the muscles of legs, belly, and buttocks.
  • 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.
  • Lying down on their back and lifting their legs in the air.

When Should I Call My Doctor?

Call your doctor if you are having periods of fainting. This is key if you:

  • Have a heart condition
  • Have a job where you or others may be at risk if you faint, such as an airline pilot, bus driver, or machinist




  • Brignole, M., Moya, A., et al. 2018 ESC Guidelines for the diagnosis and management of syncope. European Heart Journal, 2018; 39 (21): 1883-1948.
  • Choosing wisely. EBSCO DynaMed website. Available at: https://www.dynamed.com/quality-improvement/choosing-wisely.
  • Fainting. Family Doctor—American Academy of Family Physicians website. Available at: http://familydoctor.org/familydoctor/en/diseases-conditions/fainting.html.
  • Syncope in adults—approach to the patient. EBSCO DynaMed website. Available at: https://www.dynamed.com/approach-to/syncope-approach-to-the-patient.
  • 3/24/2015 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Mills, P.B., Fung, C.K., et al. Nonpharmacologic management of orthostatic hypotension: A systematic review. Archives of Physical Medicine and Rehabilitation, 2015; 96 (20): 366-375.


  • James P. Cornell, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.