If you’ve ever passed out, you are in good company. About one in every three people has experienced syncope — fainting or passing out — at some point.

Syncope happens when the brain does not get enough blood to stay awake and alert. In many cases, it is nothing dangerous, but there is no way of being sure without seeing your doctor. Syncope is also a common reason why people go to the ER. The doctor then has to determine whether it was a fainting episode (as opposed to something else, like a seizure) or because of a more serious reason.

Here’s why it might happen

  • The body has a reaction, causing the heart to beat slowly and/or the blood vessels to expand (vasovagal syncope). Stress, fear, pain, standing too long or being overheated can all bring it on. In some people it can even result from a cough or after urination or having a bowel movement. In most cases of vasovagal syncope, you have some warning that you are near fainting. This is called presyncope. These signs include dizziness, feeling hot or cold, nausea, pale skin, “tunnel-like” vision, and profuse sweating
  • A problem with the heart’s electrical system, or a medication, causes the heart to beat too slowly or too quickly to effectively supply the brain with blood
  • A blockage in blood flow out of the heart such as due to a tight valve (valve stenosis) or heart muscle disease (cardiomyopathy). In many people, especially older adults and those on heart medication, the blood pressure drops, or does not adequately increase, when they sit or stand up. This is called orthostatic hypotension. This can also result from being dehydrated, from certain medications, from alcohol consumption, from anemia (not having enough red blood cells)
  • Less common causes include a heart attack, cardiac tumour, or blood clot in the arteries supplying the lungs

How it can be diagnosed and treated

Usually syncope is not dangerous aside from the danger of suffering injury from the fall, or if you faint while driving. The doctor will need to know what you were doing and how you were feeling when you passed out, how long you were unconscious, if you were confused afterwards, if this happened to you before, what medications you are currently taking, and any medical conditions you may have.

The history often gives many important clues for the cause of syncope. The doctor will then examine you, checking your heart rate and blood pressure and listening to your heart, along with ordering blood tests, and a heart tracing (EKG) to look for possible cardiac abnormality.