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You are here : 3-RX.com > Medical Encyclopedia > Diseases and Conditions > Fainting


Alternate Names : Passing Out, Syncope, Syncopal Episode

Overview, Causes, & Risk Factors | Symptoms & Signs | Diagnosis & Tests | Prevention & Expectations | Treatment & Monitoring

Fainting is a temporary loss of consciousness and muscle tone. It is caused by not having enough blood flow to the brain.

What is going on in the body?

When there is not enough blood flow to the brain, passing out protects the brain from damage. People who faint generally lose muscle tone and fall to the ground. When someone is lying on the ground, the blood being pumped out of the heart doesn't have to fight gravity to get to the brain. Those who faint have a relaxed body, which uses less energy. This also makes it easier for the heart to pump blood to the brain.

What are the causes and risks of the condition?

The cause of fainting may be minor or it may be life-threatening. Often, no cause can be found. The following diseases and conditions may cause fainting:

  • anemia, or a low red blood cell count
  • arrhythmias, or irregular heartbeats
  • carotid stenosis, which is narrowing of the arteries supplying the brain
  • congestive heart failure, a condition in which a weakened heart fails to pump enough blood to body organs
  • hypoglycemia, which is a low blood sugar that occurs most often in people with diabetes
  • low oxygen in the blood from any cause
  • orthostatic hypotension, or low blood pressure that is caused by standing up too quickly
  • pulmonary embolus, which is a blood clot in the arteries supplying the lungs
  • Additional factors that can cause fainting are as follows:

  • dehydration
  • extreme fatigue
  • low blood pressure as a side effect of medications for high blood pressure
  • marked fear
  • pain, such as an acute injury
  • prolonged or severe coughing
  • side effects of certain medications, such as sedatives
  • straining to urinate or have a bowel movement
  • stressful events
  • There may be other causes as well. In some cases, no cause is found.


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    Fainting: Symptoms & Signs

    Author: Adam Brochert, MD
    Reviewer: Eileen McLaughlin, RN, BSN
    Date Reviewed: 09/24/01

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