What causes fainting? 41 possible conditions

What Is Fainting?

Fainting is when you lose consciousness for a short time because your brain is not getting enough oxygen. The medical term for fainting is syncope, but it is commonly known as “passing out.” A fainting spell generally lasts from a few seconds to a few minutes.

A brief feeling of lightheadedness, dizziness, weakness, or nausea sometimes precedes fainting. Some people become aware that noises are fading away, or describe the sensation as “blacking out” or “whiting out.” A full recovery generally takes only a few minutes. If there is no underlying medical condition causing you to faint, treatment is not necessarily required.

Most of the time, fainting is not a cause for concern, but in some cases, it can be a symptom of a serious medical problem. If you have no previous history of fainting, but have fainted more than once in the past month, you should consult with your doctor.

Causes of Fainting

In many cases, the cause of a fainting spell is unclear, but fainting can be triggered by a number of factors, including:

  • fear
  • emotional trauma
  • severe pain
  • a sudden drop in blood pressure
  • low blood sugar due to diabetes or from going too long without eating
  • hyperventilation (rapid, shallow breathing)
  • dehydration
  • standing in one position for too long
  • standing up too fast
  • physical exertion in hot temperatures
  • coughing too hard
  • straining during a bowel movement
  • seizures
  • consuming drugs or alcohol

Medications that can cause your blood pressure to drop also increase your likelihood of fainting. These include certain medicines to treat high blood pressure, allergies, depression, and anxiety.

If turning your head to one side causes you to faint, it may be that the bones in your neck are pinching a blood vessel.

You are at an increased risk of fainting if you have any of these conditions:

  • diabetes
  • heart blockages
  • irregular heartbeat (arrhythmia)
  • anxiety or panic attacks

Types of Fainting

The medical term for fainting is syncope. Vasovagal syncope is triggered by emotional trauma, stress, the sight of blood, or standing for a long period of time. Carotid sinus syncope happens when the carotid artery in the neck is constricted, usually after turning your head to one side or wearing a collar that is too tight. Situational syncope occurs due to strain when you are coughing, moving your bowels, urinating, or having gastrointestinal problems.

How to Prevent Fainting

If you have a history of fainting, try to learn what is causing you to faint so that 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 so that proper precautions can be taken.

When you feel the warning signs of fainting—such as lightheadedness, weakness, or the sensation of spinning—sit and put your head between your knees to help get blood to your brain, or 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 the person sit with his or her head between their knees.

Loosen tight collars, belts, or other tight 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.

If the victim is not breathing, call 911 immediately.

When Is Fainting an Emergency?

Call 911 immediately if someone has fainted and:

  • is not breathing
  • does not regain consciousness within a few minutes
  • has fallen and sustained an injury or is bleeding
  • is pregnant
  • has diabetes
  • has no history of fainting and is over age 50
  • has an irregular heartbeat
  • has complained of chest pain or pressure
  • has convulsions or has injured his or her tongue
  • has lost bowel or bladder control
  • has difficulty with speech or vision
  • is unable to move his or her limbs

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

Tests and Diagnosis

If your health is good overall and you have fainted only once, you probably don’t need to see a doctor. However, 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.

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, as well as any prescription and over-the-counter medications you take.

Depending on the findings from a physical examination, your doctor may order additional testing, including blood tests to check for chemical imbalances and anemia. Tests to check for heart problems include:

  • a Holter monitor (a portable 24-hour heart monitoring device)
  • an echocardiogram (uses sound waves to produce a moving picture of your heart)
  • an electrocardiogram (ECG) (a test that records the electrical activity of your heart)
  • an electroencephalogram (EEG) (a test that measures the electrical activity of your brain)

Treatment for Fainting

Treatment for fainting will depend on your doctor’s diagnosis. If there are no underlying medical conditions that are causing you to faint, treatment is generally not required, and the long-term outlook is good.

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See a list of possible causes in order from the most common to the least.



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Heart Attack Overview

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Low Blood Sugar (Hypoglycemia)

This condition is considered a medical emergency. Urgent care may be required.

Also known as hypoglycemia, low blood sugar can be a dangerous condition. Hypoglycemia is rare in people who are not suffering from diabetes, the chronic disease that affects the body's ability to regulate blood sugar...

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Hypotension is the medical term for low blood pressure. Low blood pressure is good in most cases, but it may lead to fatigue, dizziness, or even loss of consciousness. It can be a symptom of an underlying condition.

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Drug Allergy Overview

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A drug allergy is an allergic reaction to a medication. Your immune system identifies the drug as foreign and acts to eliminate it from your body.

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Food Allergy Basics

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Panic Disorder

Panic disorder is a condition chararcterized by persistent anxiety and recurrent panic attacks. Sweating or chills are possible signs of a panic attack.

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Anorexia Nervosa

Anorexia is an eating disorder in which obsessive worry about body weight and the food you eat can result in severe weight loss. Symptoms include constipation, missed period, and thinning hair.

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Abnormal Heart Rhythms

This condition is considered a medical emergency. Urgent care may be required.

An abnormal heart rhythm (arrhythmia) is a change in the heart's beating pattern. There are many different types with different causes and effects. Possible symptoms are feeling faint, chest pain, and sweating.

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Ventricular Tachycardia

This condition is considered a medical emergency. Urgent care may be required.

Ventricular tachycardia (VT) is a very fast heartbeat caused by a malfunction of the heart's pacing mechanism. VT can occur with or without heart disease. Symptoms include fainting, dizziness, and more.

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Pulmonary Embolism

This condition is considered a medical emergency. Urgent care may be required.

A pulmonary embolism is a blood clot that affects blood flow to the lungs. It can damage part of the lung due to restricted blood flow, decrease blood oxygen. The most common symptom is shortness of breath.

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The Catastrophy of Cardiac Tamponade

This condition is considered a medical emergency. Urgent care may be required.

Cardiac tamponade is a serious medical condition in which fluids fill the space between the sac around the heart and the heart muscle, creating pressure. Symptoms include anxiety, short breath, fainting, and more.

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Sick Sinus Syndrome

Sick sinus syndrome (SSS) is a general name for a group of disorders caused by a malfunctioning sinus node. The sinus node acts as a pacemaker inside the heart. Sinus rhythm (the normal beating of the heart) i...

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Peripheral Neuropathy

Peripheral neuropathy occurs when nerves malfunction because they're damaged or destroyed. You'll notice a tingling, numbness, or weakness, and possibly sweating, constipation, or diarrhea.

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Alcoholic Liver Disease

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Ectopic Pregnancy

This condition is considered a medical emergency. Urgent care may be required.

Ectopic pregnancies occur when a fertilized egg fails to attach to the uterus. In most ectopic pregnancies, the egg will attach to the fallopian tubes. Less common, it may also attach to the abdominal cavity or cervix...

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Atrial Fibrillation and Flutter

Atrial fibrillation and atrial flutter are irregular heart rhythms that occur when the upper chambers of your heart (the atria) beat too fast.Atrial fibrillation can be sustained or can occur in bursts. It creates a...

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Paroxysmal Supraventricular Tachycardia (PSVT)

This condition is considered a medical emergency. Urgent care may be required.

Paroxysmal supraventricular tachycardia (PSVT) is a faster-than-normal heart rate. It can last from a few minutes to several hours. PSVT is a fairly common type of (arrhythmia) that can occur in a person of any age.

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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.
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