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
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These health problems may also cause fainting:

  • Orthostatic hypotension—low blood pressure when standing
  • Anemia—low iron in the blood
  • Hypoglycemia—low blood glucose
  • Seizures
  • Stroke or transient ischemic attack
  • Heart conditions

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

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

When Should I Call for Medical Help Right Away?

Call for emergency medical services right away if you have:

  • Weakness or numbness of the face, arm, or leg
  • Confusion
  • Loss of balance
  • Movement problems
  • Vision problems
  • Severe headache
  • Rapid, irregular heartbeat; chest pain


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.

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.

Edits to original content made by Denver Health.