Fainting is a sudden, temporary loss of consciousness. And while passing out can be scary and disorienting, the good news is that most people recover quickly and it’s usually not a sign of a serious health condition. In fact, fainting is fairly common.

So, what causes fainting? What does it feel like when you’re about to faint? What should you do if you’re with someone who feels like they’re going to pass out or does faint? And when should you see a doctor?

We answer all those questions and more below.

What causes fainting? A drop in blood flow to the brain.

When the brain isn’t getting the blood – and therefore the oxygen – it needs, this drop in blood flow causes you to lose consciousness and fall down. While this can be concerning, falling is actually 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’re lying flat, blood returns to the brain rapidly. That’s why most people wake up pretty quickly after passing out.

Reasons why a person may faint

The medical term for fainting is syncope (pronounced SING-kuh-pee). And usually, a fainting episode isn't a sign of a serious underlying condition. Instead, fainting is often caused by:

  • The vasovagal reflex (vasovagal syncope), which causes your heart rate to slow and the blood vessels to widen. This reflex can be triggered by many things, including stress, pain, fear, coughing, holding your breath and urinating. The vasovagal reflex accounts for most fainting episodes.
  • 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.

A person who faints usually will not suffer any long-term health effects. But we recommend that you talk with your primary care doctor if you faint and you’re not sure why.

Signs you’re about to pass out

While a fainting spell can happen quickly, there are often warning signs just before you pass out. The feeling that you’re about to faint (also known as pre-syncope) may include:

  • Weakness, dizziness or lightheadedness
  • Shortness of breath
  • Nausea or vomiting
  • Sudden sweating or clammy skin
  • Paleness
  • Blurring or fading vision
  • Seeing spots or lights
  • A fast or irregular heartbeat

How to prevent fainting

If you feel faint, or 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:

  • Lie down with your feet elevated to help blood get back to your brain.
  • Sit with your head between your knees if you can’t lie down.
  • Move around to help your blood circulate after standing or sitting for a long time. If you’re seated, flex your legs or cross and uncross them regularly.
  • Change your position or stand up, but do so slowly.
  • Move to a cooler environment with fresh air if you’re in a hot or stuffy space.

If you have a history of passing out or feeling faint, do your best to avoid situations that might cause you to faint. Make sure to stay hydrated throughout the day, especially on hot days and before, during and after exercise. Also, try to avoid spending long periods in cramped, crowded and hot environments.

What to do if someone faints

Helping someone who faints is similar to preventing fainting in the first place. Here’s how you can care for someone who has fainted:

  • If someone looks lightheaded or says they’re not feeling well and may faint, have them lie down or sit with their head between their knees.
  • 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 tight clothing.
  • If they’re pregnant or if they’ve vomited, gently turn them onto their side while unconscious.
  • After they wake up, have them stay lying down or sitting for a while longer until they’re feeling better.
  • Give them water and juice to help them stay hydrated and increase their blood sugar. You can also offer them a cool, moist cloth for their face or neck, and then move them to a cooler, better ventilated environment, if possible.
  • Help them stand up slowly if they need to be moved, and have them sit down and rest again afterwards.

When does fainting become more serious? Here’s what you should know.

Fainting may be a sign of a serious problem or underlying condition if it has certain characteristics. Call 911 immediately if you or someone else who faints:

  • Did so during exercise or a vigorous activity
  • Did so without warning or while lying down
  • Gets injured
  • Had shortness of breath, chest pain, or a racing or irregular heartbeat
  • Had numbness, tingling or convulsions (rapid, involuntary movements)
  • Has a headache, blurred vision, or difficulty talking or moving after waking up
  • Isn’t responsive within a few minutes
  • Is pregnant, over age 50, has diabetes or a heart condition

A fainting spell usually isn’t cause for concern, but don’t ignore it

While fainting is common and usually not a sign of a more serious underlying condition, it’s worth checking in with your primary care doctor or clinician if you:

  • Recently fainted and aren’t sure why
  • Are experiencing new symptoms related to fainting
  • Have passed out more than once recently

With their understanding of your overall health, family history and any medicines you’re taking, your doctor can help you find out what might have caused you to faint and help you avoid fainting in the future.