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Fainting: Uncertain Cause

Fainting (syncope) is a temporary loss of consciousness. It's often associated with a loss of postural tone. It’s also called passing out. It occurs when blood flow to the brain is less than normal. There are other causes of fainting, too. Near-fainting (near-syncope) is very similar to fainting, but you don’t fully pass out.

Most commonly, fainting is for reasons that aren't necessarily serious or life-threatening, although you may still get injured. Common triggers of less serious types of fainting include:

  • Sudden fear

  • Pain

  • Nausea

  • Emotional stress

  • Overexertion

Suddenly standing up after sitting or lying for a long time can also cause fainting.

More serious causes of fainting include:

  • Very slow or very fast heartbeat (arrhythmia)

  • Other types of heart disease, such as heart valve disease or coronary artery disease

  • Dehydration

  • Loss of blood

  • Seizure

  • Stroke

  • Ruptured blood vessel in the brain

Taking too much high blood pressure medicine can also cause low blood pressure and fainting.

Your healthcare provider may be able to tell why you are fainting by reviewing your health history and hearing about your fainting episodes. If the cause of your fainting remains unknown or if your healthcare provider is concerned about a more serious cause he or she may determine that you need further testing. Testing may include:

  • Echocardiogram. This will take ultrasound pictures of your heart to evaluate the heart's structure and function

  • Stress test. This will check for abnormalities with you heart function or heart rhythm with exercise

  • Tilt table test. This evaluates for changes in blood pressure or heart rate when going from a laying position to standing

  • Heart monitoring. This will evaluate for heart rhythms that are too slow or too fast that may be the cause of your fainting

  • Lab tests. This can check for abnormalities in electrolytes, blood counts and other things

Home care

Follow these guidelines when caring for yourself at home:

  • Rest today. You may go back to your normal activities when you are feeling back to normal. It's best to stay with someone who can check on you for the next 24 hours to watch for another episode of fainting.

  • If you become lightheaded or dizzy, lie down right away and try to prop your feet above the level of your head. Or sit with your head between your knees.

  • Because the provider doesn’t know the exact cause of your fainting or near-fainting spell, it’s possible for you to have another spell without warning. Because of this, don’t drive a car or operate dangerous equipment until your healthcare provider says it's OK to do so. Don’t take a bath alone. Use a shower instead. Don’t swim alone until your healthcare provider says that you are no longer in danger of having another fainting spell.

Follow-up care

Follow up with your healthcare provider, or as advised.

When to seek medical care

Call your healthcare provider right away if any of these occur:

  • Another fainting spell that’s not explained by the common causes listed above

  • Pain in your chest, arm, neck, jaw, back, or abdomen

  • Shortness of breath

  • Severe headache or seizure

  • Blood in vomit or stools (black or red color)

  • Unexpected vaginal bleeding

  • Your heart beats very rapidly, very slowly, or irregularly (palpitations)

Also call your provider if you have signs of stroke:

  • Weakness in an arm or leg or on one side of the face

  • Trouble speaking or seeing

  • Extreme drowsiness, confusion, dizziness, or fainting

Online Medical Reviewer: Lu Cunningham
Online Medical Reviewer: Quinn Goeringer PA-C
Online Medical Reviewer: Steven Kang MD
Date Last Reviewed: 6/1/2019
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