Fainting: Causes, Treatment & Diagnosis

By Terez Malka, MD
Medically reviewed checkmarkMedically reviewed
July 21, 2022

A person experiences fainting when a lack of oxygen to the brain causes momentary loss of consciousness.

In most instances, fainting is nothing to be alarmed by.

It can be caused by fear, dehydration, anxiety, or even emotional stress, and should last only a few seconds to a couple minutes. 

If you’ve had several fainting episodes recently, check in with a medical professional, as fainting may be an indicator of an underlying health issue.

In this article, I will cover the various types of fainting, potential causes, warning signs, and more.

What is Fainting (Syncope)?

Also referred to as “passing out,” fainting (or syncope) is a momentary loss of consciousness caused by a lack of oxygen to the brain from a sudden drop in blood flow.

This is typically short-lived, and lasts just a few seconds or minutes before you regain consciousness.

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Types of Syncope

There are several different types of syncope a person may experience.

The type of syncope you have depends on the cause.

A few of the most common types of syncope include:

Cardiac Syncope

Cardiac syncope occurs when an underlying heart issue reduces the flow of blood and oxygen to the brain.

This type of syncope can be caused by pre-existing heart conditions including:

  • Heart rhythm abnormalities
  • Heart attack
  • Heart failure
  • A blood clot in the lungs (pulmonary embolism)
  • Narrowing of a heart valve

Carotid Sinus Syncope

Also known as carotid sinus hypersensitivity, carotid sinus syncope typically occurs in older adults and is triggered by a reflex caused when pressure is felt on the carotid artery in the neck. 

A sharp twist of the neck when wearing a tight collar that presses on the artery, for instance, can lead to carotid sinus syncope.

Vasovagal (situational) Syncope

The most common type of fainting, vasovagal syncope, is a result of your body’s overreaction to a trigger, like the sight of blood or emotional distress, or as a result of standing for long periods of time or heat exposure. 

Your body has a reflex response to these situations that causes temporary low blood pressure and a slow heart rate, which causes you to faint.

Situations that can cause this include: 

Causes

While syncope is sometimes caused by an underlying medical issue, that’s not always the case.

There are many factors that can lead to fainting, even in otherwise healthy individuals.

These include:

  • Dehydration – When you don’t drink enough water or consume enough electrolytes, your blood pressure can drop and may trigger you to faint. 
  • Vasovagal attack – These attacks are caused by a quick drop in blood pressure that’s been triggered by fear, emotional distress, or certain physical situations like prolonged standing, heat, or being dehydrated. This causes your heart rate to drop and limits the blood flow to your brain.
  • Anxiety – A common symptom of people who suffer from anxiety disorders, fainting can occur as a result of hyperventilation. This causes you to breathe in too much oxygen and breathe out too much carbon dioxide, which reduces the blood flow to your brain and triggers a fainting episode. Anxiety can also trigger a vasovagal syncope episode.
  • Postural hypotension – When you sit up or stand up too quickly, your blood pressure drops, resulting in less blood flow to your brain which can cause fainting.
  • Heart problems – Pre-existing heart conditions, like heart rhythm disturbances or severe  hypotension, can cause cardiac syncope.
  • Hyperventilation – When a person’s carbon dioxide blood levels fall from breathing too quickly, the result is a decrease of blood flow to the brain, which can cause fainting.
  • Neurological conditions – Processes within the brain such as a stroke (cerebrovascular accident), bleeding in the brain, and seizures, can all cause loss of consciousness and fainting. These types of events usually have additional symptoms besides just fainting.
  • Blood sugar – Hypoglycemia (or low blood sugar levels) can make you feel shaky or dizzy, causing you to lose consciousness.
  • Drugs or alcohol – Drinking alcohol or using recreational drugs can cause your blood pressure to lower and restrict blood flow to the brain, which can trigger a fainting episode.
  • Certain medications – Medications that reduce blood pressure, heart medicine, and others can all cause dizziness or fainting as a side effect.

Warning Signs

Most of the time, people feel warning signs before experiencing a fainting episode.

Some of the feelings you may experience include: 

Some people also experience loss of vision or vision changes, like blacking out, whiting out, or “seeing stars.”

Diagnosis

If you’ve fainted multiple times, make an appointment with your medical professional for a diagnosis.

They’ll give you a physical exam, review your medical history, and ask detailed questions about your fainting episode.

If necessary, your doctor may also issue one or more of the following tests:

  • Blood work to test for metabolic changes in your body or anemia
  • Electrocardiogram (EKG) to check the electrical activity of your heart
  • Echocardiogram (ECG) to see the function of your heart by ultrasound
  • Exercise stress test to record your heart’s response to exercise
  • Tilt table test to test your blood pressure and heart rate while your body is tilted to different levels
  • Ambulatory monitor to record your heart rate and rhythm over a period of time
  • EEG to look at brain wave activity to check for seizures
  • Brain imaging using CT or MRI to look for neurological causes 

Treatment

If you, or someone you know faints, provide the following fainting first aid:

Treatment for yourself:

  • Lie on the ground, or put your head as close to the ground as possible
  • Elevate your feet to encourage blood flow to your head
  • Stay lying down for 10 minutes and slowly sit up when you start to feel better

Treatment for others:

  • Help the person lie down on the ground
  • Check to make sure they’re breathing, and if they’re not, call 911 immediately
  • If unconscious, roll them onto their side
  • Elevate their feet
  • Loosen any restrictive clothing, like belts or neck ties

While the occasional fainting episode won’t require treatment, see your doctor for an evaluation if you frequently faint.

Together, you can determine what treatment is best suited for you.

Prevention

Vasovagal syncope can’t always be avoided.

But to prevent the onset of situational syncope, do the following:

  • Stay hydrated by drinking enough water daily
  • Avoid skipping meals and eat a healthy snack when you feel hungry between meals
  • Avoid standing still in one place for too long, by moving your legs or pacing if necessary
  • On hot days, stay inside or in a shaded area
  • Take all medications as prescribed and let your doctor know if you feel any fainting symptoms from your medication
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When to See a Medical Provider

In most scenarios, a healthy person doesn’t need to speak with a healthcare provider after a fainting incident. 

However, if you’ve experienced a syncope episode and continue to experience symptoms after you’ve regained consciousness, seek medical attention.

These symptoms may include:

Those who are pregnant, have high blood pressure, or have diabetes should also inform their doctor if they experience any fainting or loss of consciousness.

You should also seek medical attention if you sustain a falling injury from fainting, remain unconscious longer than a few minutes, or experience frequent fainting spells.

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Frequently Asked Questions

What are the warning signs of fainting?
If you’re about to faint, you’ll likely experience a warning sign. Early indicators of fainting include, blurred vision, dizziness, headache, nausea or vomiting, seeing spots, shortness of breath, sweating, tinnitus (ringing in the ears), and weakness.
What causes a person to faint?
Fainting is caused by a sudden drop in blood pressure, which decreases the blood flow to the brain. It could be caused by a pre-existing medical issue, or any number of factors such as anxiety, dehydration, drug or alcohol use, heart conditions, hyperventilation, low blood sugar levels, some neurological conditions, and prescribed medications.
What does fainting feel like?
If you’re about to faint, you’ll experience warning symptoms that may include feeling dizzy, nauseous, or lightheaded. You may also momentarily lose your vision and “black out” or “white out.” Additionally, you may lose muscle control.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Terez Malka, MD

Dr. Terez Malka is a board-certified pediatrician and emergency medicine physician.