What Causes Fainting?

Medically reviewed by Suzanne Falck, MD on February 8, 2018Written by Ann Pietrangelo

Fainting happens when you lose consciousness for a short amount of time because your brain isn’t getting enough oxygen. The medical term for fainting is syncope, but it’s more commonly known as “passing out.” A fainting spell generally lasts from... Read More

Understanding fainting

Fainting happens when you lose consciousness for a short amount of time because your brain isn’t getting enough oxygen.

The medical term for fainting is syncope, but it’s more commonly known as “passing out.” A fainting spell generally lasts from a few seconds to a few minutes.

Feeling lightheaded, dizzy, weak, or nauseous sometimes happens before you faint.

Some people become aware that noises are fading away, or they describe the sensation as “blacking out” or “whiting out.”

A full recovery usually takes a few minutes. If there’s no underlying medical condition causing you to faint, you may not need any treatment.

Fainting isn’t usually a cause for concern, but it can sometimes be a symptom of a serious medical problem. If you have no previous history of fainting and you’ve fainted more than once in the past month, you should talk to your doctor.

Causes of fainting

In many cases, the cause of fainting is unclear.

Fainting can be triggered by a number of factors, including:

Medications that can cause your blood pressure to drop also increase your chance of fainting. These include certain medications used to treat:

If turning your head to one side causes you to faint, it’s possible that the sensors in the blood vessel in your neck are extra sensitive. This sensitivity can cause you to faint.

You’re also more likely to faint if you have any of these conditions:

Types of fainting

There are several types of syncope. Three common types include:

  • Vasovagal syncope. Vasovagal syncope involves the vagus nerve. It can be triggered by emotional trauma, stress, the sight of blood, or standing for a long period of time.
  • Carotid sinus syncope. This type happens when the carotid artery in the neck is constricted, usually after turning your head to one side or wearing a collar that’s too tight.
  • Situational syncope. This type occurs due to straining while coughing, urinating, moving your bowels, or having gastrointestinal problems.

How to prevent fainting

If you have a history of fainting, try to learn what’s causing you to faint so you can avoid those triggers.

Always get up slowly from a sitting or lying-down position. If you tend to feel faint at the sight of blood when getting your blood drawn or during other medical procedures, tell your doctor. They can take certain precautions to prevent you from fainting.

Lastly, don’t skip meals.

Feeling lightheaded and weak and having the sensation of spinning are warning signs of fainting. If you notice any of these signs, sit and put your head between your knees to help get blood to your brain.

You could also lie down to avoid injury due to falling. Don’t stand up until you feel better.

What to do when someone faints

When someone near you faints, you can encourage blood flow to their head by raising their feet above the level of their heart.

Alternatively, you can have them sit with their head between their knees.

Loosen tight collars, belts, and other restrictive clothing. Keep the person lying down or sitting for at least 10 to 15 minutes. A cool, quiet place is best.

A cool drink of water may also help. Learn more about first aid tips for unconsciousness.

If the person isn’t breathing, immediately call 911 or your local emergency services.

When is fainting an emergency?

You should call 911 or your local emergency services immediately if someone has fainted and:

Follow the instructions of the 911 operator or emergency dispatcher. You may need to perform rescue breathing or CPR while awaiting help.

Tests and diagnosis

If you have no prior history of fainting and have fainted multiple times, your doctor will want to determine if an underlying medical condition is the cause.

Even people who only pass out once should at least get an electrocardiogram (ECG or EKG), which records the electrical activity of your heart.

Tell your doctor about the specific circumstances of your fainting spell, such as what you were doing and how you felt immediately before fainting.

Be prepared to give your doctor a complete medical history, including information about previously diagnosed conditions and any prescription and over-the-counter (OTC) medications you take.

Depending on the findings from a physical examination, your doctor may order additional tests.

Diagnosis typically starts with EKG. Other tests that may be used to find out why you passed out include:

  • Holter monitor. This is a portable heart-monitoring device that you wear for at least 24 hours.
  • Echocardiogram. This test uses sound waves to produce a moving picture of your heart.
  • Electroencephalogram. The electroencephalogram (EEG) measures the electrical activity of your brain. After listening to a description of your symptoms, your doctor will usually be able to tell whether you fainted or had a seizure. They’ll perform the EEG if they’re unsure.

In some instances, you may receive a head CT scan. This imaging study checks for bleeding in the brain.

It doesn’t generally help figure out the cause of fainting, though. It’s only helpful when a head injury has occurred and there’s concern for bleeding.

Treatment and outlook

Treatment for fainting will depend on your doctor’s diagnosis.

If there are no underlying medical conditions that are causing you to faint, you generally won’t need treatment and the long-term outlook is good.

Medically reviewed by Suzanne Falck, MD on February 8, 2018Written by Ann Pietrangelo

41 possible conditions

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This feature is for informational purposes only and should not be used to diagnose. Please consult a healthcare professional if you have health concerns.

Medically reviewed by Suzanne Falck, MD on February 8, 2018Written by Ann Pietrangelo
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