Fainting: Uncertain Cause

Fainting (syncope) is a temporary loss of consciousness. It's often related to 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.

In most cases, fainting occurs for reasons that may not be serious or life-threatening. But it may still be dangerous if you fall or if it occurs while driving. 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.

• Stroke.

• Ruptured blood vessel in the brain.

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

Your health care 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 provider is concerned about a more serious cause, you need further testing. Testing may include:

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

• Stress test. This will use exercise to check for problems with your heart function or heart rhythm.

• Tilt table test. This checks for changes in blood pressure or heart rate when going from lying down to standing.

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

• Lab tests. This can check for problems with electrolytes, blood counts, and other things.