It can be unsettling to faint – or to see someone else fainting. But the good news is that fainting (also called passing out or blacking out) isn’t usually a sign of a serious health problem.

When someone faints, they’re experiencing a brief loss of consciousness that can be caused by a variety of factors, many of which are short-term.

In this post, we’ll cover the causes of fainting, ways to prevent it, how to help someone else who has fainted, and when it’s a good idea to talk to a doctor about your concerns.

What causes fainting?

Put simply, fainting happens when there is a drop in blood flow to the brain. When the brain isn’t getting the blood (and importantly, the oxygen) it needs, it causes you to lose consciousness and fall down. Fascinatingly (and perhaps counterintuitively), falling is the body’s way of trying to recover. When you’re standing up, it takes a lot of effort to fight gravity and pump blood all the way up to your head. But when you fall down and you’re lying flat, blood returns to the brain rapidly. That’s why most people wake up pretty quickly after fainting.

The medical term for fainting is syncope (pronounced SING-kuh-pee). Fainting once is usually not a big cause for concern. The most common causes of fainting are usually not signs of a more serious illness. In these cases, you faint because of:

  • The vasovagal reflex, which causes the heart rate to slow and the blood vessels to widen (or dilate). This reflex can be triggered by many things, including stress, pain, fear, coughing, holding your breath, and urinating.
  • Orthostatic hypotension, or a sudden drop in blood pressure when you change position. This can happen if you stand up too fast, get dehydrated, or take certain medicines, such as ones for high blood pressure.

Some people know when they are going to faint because they have symptoms beforehand, such as feeling weak, nauseated, hot or dizzy. After they regain consciousness, they may feel confused, dizzy or ill for a while but recover fairly soon.

A person who faints usually will not suffer any long-term health effects. However, we recommend that you see your doctor after a fainting spell.

What can you do to avoid fainting?

If you know you tend to faint at certain times (such as when you get a shot or have blood drawn), it may help to:

  • Sit with your head between your knees or lie down if you feel faint or have warning signs such as feeling dizzy, lightheaded, weak, warm or sick to your stomach.
  • Drink plenty of fluids so you don't get dehydrated.
  • Stand up slowly.

What to do if someone faints

It can be alarming when someone faints. But in most cases, it isn’t caused by anything that’s life threatening. Here’s what you can do to help someone who’s fainted:

  • Preventively, if someone looks lightheaded or says they’re not feeling well and may faint, have them sit with their head between their knees or lie down.
  • If they’ve fainted, lay the person down and elevate their feet. Most people will recover quickly after fainting once they lie down as more blood flows to the brain. It also helps to loosen any constrictive clothing.
  • After they wake up, have them stay lying down or sitting for a while longer until they’re feeling better.
  • Give them water to help them stay hydrated.
  • Help them stand up slowly – and it’s a good idea for them to sit down and rest again until they’re feeling back to normal.

Fainting may be the sign of a serious problem or underlying condition if:

  • It happens often in a short period
  • It happens during exercise or a vigorous activity
  • It happens without warning or if it happens when you are already lying down. (When fainting is not serious, a person often knows it is about to happen and may vomit or feel hot or queasy.)
  • You are losing a lot of blood
  • You feel short of breath
  • You have chest pain
  • You feel like your heart is racing or beating unevenly (palpitations)
  • It happens along with numbness or tingling on one side of the face or body

When to talk to a doctor about fainting

It’s always the right time to talk to a doctor if you have a health concern. And if you’ve fainted and have questions about it, or if you’ve fainted more than once recently, it’s a good idea to talk with your primary care doctor. With their understanding of your overall health, family history and medicines you’re taking, they can listen to your symptoms and help you find out what might have caused you to faint.

If you’ve fainted more than once lately or if fainting is very out of the ordinary for you, your doctor may want to do some tests to determine whether your fainting symptoms could be caused by an underlying condition that should be addressed.