Vasovagal Syncope: The Most Common Cause of Fainting

Vasovagal syncope occurs when your body reacts so strongly to a trigger—like having blood drawn or being scared—that your heart rate and blood pressure plummet and you faint.

An episode of fainting from vasovagal syncope usually only lasts seconds to minutes. For example, fainting while sitting in a chair while having your blood taken could be an episode of vasovagal syncope.

On its own, vasovagal syncope is not something to worry about dying from. However, the suddenness of the reaction and temporary loss of consciousness that follows can lead to dangerous falls and injuries.

This article explains the different phases of a fainting episode due to vasovagal syncope. It also discusses the symptoms and causes of the condition, as well as how it can be treated and prevented.

vasovagal syncope
Verywell / Brooke Pelczynski

What Are Symptoms of Vasovagal Syncope?

Fainting from a vasovagal response can be sudden and unexpected. However, you may have warning signs a few seconds or minutes before a fainting episode. 

The signs leading up to fainting are called the prodrome of syncope. The symptoms that come on after you regain consciousness are called postdromal symptoms.

Prodromal Symptoms

Prodromal symptoms of syncope can include:

  • Lightheadedness
  • Ringing or buzzing in the ears
  • Visual disturbances, such as "shimmering" vision or tunnel vision
  • Sudden sweating
  • Sudden nausea

The prodromal symptoms are sometimes followed by a sensation of "graying out," in which the colors and light around you get dim. The visual changes are followed by a loss of consciousness.

The time between when prodromal symptoms come on and when you actually pass out can range from a few minutes to just a second or two.

Vasovagal Episode Symptoms

Episodes of vasovagal syncope have several key symptoms and features that make them different from other causes of fainting:

  • The episodes almost always occur while you’re standing or sitting up. This is because more blood goes to your legs when you are standing and your blood pressure drops. Fainting almost never happens when someone is lying down.
  • You will usually regain consciousness a few seconds after falling or being helped to the ground. This is because your normal blood pressure is restored in the lying-down position.
  • Being held up won’t help. If someone tries to hold you up during a vasovagal episode, being in a standing position can actually prolong the time you are unconscious.

Postdromal Symptoms

After an episode of vasovagal syncope, many people will feel nauseous, dizzy, and very tired for a few hours. These symptoms can last for a day or longer.

You are at risk of fainting again until these symptoms go away. You will need to avoid driving, climbing ladders, or doing anything that would be dangerous for you or others around you should you pass out. 

You should also be aware of the warning signs of another fainting episode and take steps to try to prevent it. 

What to Do

If you think you might faint from vasovagal syncope, there are some steps you can take to stay safe.

Stay calm but know that you don’t have long to keep a fainting spell from happening—maybe five to 10 seconds.

  • If you feel like you’re about to faint, you might be able to prevent it by lying down with your legs up or sitting in a chair with your head between your knees. Wait until you feel better before trying to get up.
  • If there’s no chair or surface around to sit on, try to lower yourself down to the floor and lie down. The goal is to make sure that you are as close to the ground as possible so that you won’t get hurt on the way down if you pass out. 
  • If your clothes are tight (for example, you have a scarf around your neck or a tightly buttoned-up shirt) try to loosen them up. 

If you faint because you have vasovagal syncope, there are a few things you can do to take care of yourself after it happens:

  • If you are not injured, lay down with your feet slightly elevated (use a pillow, a coat, whatever is handy). Stay in this position for about 10 minutes. Don’t get up too fast, as you could faint again. 
  • Try to rest somewhere with fresh air that’s not too warm.
  • Take slow, deep breaths. Try to avoid hyperventilating if you’re anxious. 
  • If you think you might be dehydrated or have low blood sugar, you may need a glass of water or juice and a snack. If you think that your blood pressure is too low, eating something salty or having an electrolyte drink may help.

First Aid for Fainting

If you think you may have gotten hurt when you fell, do not move. Call for help if you are able, and wait for emergency responders to arrive. You should also call 911.

Knowing first aid for fainting is useful even if you don’t have vasovagal syncope yourself—you never know when someone around you may faint and need help.

If you see somebody faint, lay the person on their back and raise their legs above the level of their heart. Loosen any belts, collars, or other tight clothing/accessories and call for professional medical help.

What Causes Vasovagal Syncope?

Vasovagal syncope happens when something triggers the vasovagal reflex, which causes blood vessels to widen (dilate) suddenly. Dilation of the blood vessels causes a lot of the blood in the body to pool in the legs.

The pooling of blood is accompanied by a slowing heart rate, which leads to a drop in blood pressure. If the drop in blood pressure is big enough that the brain isn’t getting the oxygen it needs, a person faints. 

Common Triggers

Vasovagal syncope is more likely to happen when a person is dehydrated, sick, doing vigorous exercise, or sleeping through the night without drinking water. Common triggers of vasovagal syncope include:

  • Sudden, severe pain
  • Having your blood drawn
  • Being exposed to a traumatic sight or event
  • High levels of stress, anxiety, or fear
  • Straining while urinating or having a bowel movement
  • Severe coughing
  • Hyperventilation (breathing too fast)
  • Standing still for long periods of time
  • Overexerting yourself in hot weather
  • Excessive alcohol or substance use

There’s a strong link between vasovagal syncope and anxiety, and it can have a cyclical effect. Strong feelings of stress and anxiety can be a trigger for syncope, and repeated fainting spells can raise anxiety levels and lead to mental health conditions like depression.

Who’s at Risk for Vasovagal Syncope?

The reflex that causes vasovagal syncope can affect anyone and fainting spells are common. However, some people are more at risk of fainting from vasovagal syncope than others. 

Young Adults and Adolescents

Vasovagal syncope can occur at any age but is more common in adolescents and young adults. 

More than 85% of fainting episodes in people younger than 40 years of age are from vasovagal syncope and about half of fainting episodes in older adults are caused by it.

Recurrent Syncope

Some people are more likely to have vasovagal episodes than others and might be easily triggered. 

People who are just more prone to fainting spells generally notice they start when they’re in their teens and can be triggered by a variety of things, like the sight of blood. 

Dysautonomia

Some people have frequent vasovagal syncope that is so hard to treat that they become disabled by it. Often, the fainting is linked to dysautonomia, an imbalance of the autonomic nervous system.

The autonomic nervous system controls body functions like our heartbeat and breathing. Dysautonomia makes a person more prone to the vasovagal reflex that causes syncope.

Fainting is usually accompanied by other symptoms of dysautonomia, such as:

  • Abdominal bloating or cramps
  • Diarrhea
  • Constipation
  • Extreme fatigue
  • Various aches and pains

Other Causes of Fainting

Vasovagal syncope is not the only reason people faint. In fact, there are several health conditions that can cause fainting:

  • Orthostatic hypotension is a condition where your blood pressure falls when you stand up, making you feel dizzy or lightheaded. This can lead to fainting.
  • Postural orthostatic tachycardia syndrome (POTS) is a condition where you get lightheaded and have heart palpitations (irregular beats) when you stand up, and you may pass out. 
  • Low red blood cell count (anemia) can cause fainting because red blood cells help your body get oxygen. 
  • Seizures can lead to fainting and a loss of consciousness. 
  • Heart conditions or problems like arrhythmias can cause fainting. 
  • Diabetes can cause your blood sugar levels to be too high or too low, which can make you faint. 
  • Conditions that affect your brain, like a transient ischemic attack, can make you faint if certain arteries are affected.
  • Lung problems that cause your blood to not have enough oxygen (hypoxia) can make you faint. Likewise, breathing too fast or too hard (hyperventilation) can make you pass out and can happen when you’re scared or anxious.
  • Straining from coughing or having a bowel movement can cause fainting. 
  • Standing up for too long, especially if you lock your knees, can cause you to faint. 
  • Dehydration can make you faint, especially if you’ve been exercising hard or spending time in hot weather.
  • Certain medications and substances can cause fainting. 

When to See a Healthcare Provider

It’s a good idea to contact your healthcare provider after you’ve fainted unexpectedly—especially if you’ve never fainted before. 

If you've been diagnosed with vasovagal syncope, call your provider if you are pregnant or have recurrent episodes of fainting. 

Get medical attention right away if you have other symptoms before you faint, such as:

  • Blurred vision
  • Chest pain
  • Confusion
  • Trouble talking
  • Shortness of breath
  • Irregular heartbeat

How Is Vasovagal Syncope Diagnosed?

Your healthcare provider will review your symptoms, medical history, and family history. They will then ask about the events leading up to your fainting episode.

The physical exam of people with vasovagal syncope is usually completely normal. Your provider might want to do some other basic tests to rule out more serious causes of fainting, including:

  • Blood tests
  • Listening to your heart and breathing sounds
  • Measuring your blood pressure 
  • Checking your brain function with neurological tests
  • Heart function tests (electrocardiogram, Holter monitor, echocardiograms, and/or stress test) 

Sometimes, specific tests are needed to diagnose vasovagal syncope or tell it apart from another cause of fainting. For example, you might need to have a tilt table study to help distinguish vasovagal syncope from orthostatic hypotension.

For the test, you are strapped to a table that tilts upward to put you in a position similar to standing. This allows the provider to measure your heart rate and other factors that may be responsible for fainting episodes. 

Your provider may want to do imaging tests like an X-ray, MRI, or CT scan if they want to check a specific part of your body more closely, like your chest or head, though these tests are less commonly used to diagnose fainting.

How Is Vasovagal Syncope Treated?

People who have a single, one-time episode of vasovagal syncope generally do not need any medical treatment. If you have recurrent fainting episodes, you should talk to your provider about them.

Fainting episodes can come at inconvenient, impractical, and unsafe times. While vasovagal syncope is not life-threatening, the consequences of fainting can be. For example, falls can cause serious injuries, and fainting behind the wheel could lead to a car accident. 

Treatment for vasovagal syncope usually includes a combination of strategies like medication and exercise.

Medications

Certain medications can help regulate blood pressure and heart rate and may help people with vasovagal syncope, including:

  • Midodrine (causes narrowing of the blood vessels)
  • Norpace (disopyramide) (regulates your heartbeat)
  • Selective serotonin reuptake inhibitors (a type of antidepressant)
  • Theophylline (used to treat asthma)

Exercises

An episode of vasovagal syncope can sometimes be stopped by immediately doing exercises that tense the muscles. When the muscles are tense, it reduces blood vessel dilation and increases the amount of blood being returned to the heart.

Examples of exercises that may help prevent fainting from vasovagal syncope include: 

  • Crossing your legs and squeezing them together
  • Tensing your arms with clenched fists
  • Tensing your leg muscles, abdomen, and buttocks
  • Squeezing a rubber ball

If you have recurrent syncope, ask your healthcare provider before starting a fitness plan. You may need to have stress testing and other exams to determine how much exercise you can do safely.

A pacemaker (a device that regulates the heartbeat) used to be suggested for people with vasovagal syncope, but research has shown it is not helpful.

How Can You Prevent Vasovagal Syncope?

If you’ve had one or two episodes of vasovagal syncope, you’ve probably learned to spot the warning signs. You may even be able to prevent an episode by lying down and elevating your legs.

However, trying to "fight off" an episode of vasovagal syncope by forcing yourself to stay standing or sitting up and "willing yourself" not to faint almost never works.

The best thing you can do to prevent fainting is to avoid your triggers—for example, excessive heat, stress, dehydration, pain, and prolonged standing. If you have low blood pressure, consider talking to your provider about whether increasing your salt intake could help you avoid fainting episodes.

Summary

Vasovagal syncope is the main cause of fainting. It happens when someone is upright and their blood pressure drops fast, causing them to temporarily lose consciousness (pass out). 

While fainting is often a one-time event, it can be a recurrent problem for some people. 

Vasovagal syncope can be triggered by having your blood drawn or an emotionally upsetting event. Medications and/or certain exercises can help people manage fainting spells related to vasovagal syncope, but the most important thing is learning your triggers and trying to avoid them. 

If you have fainted or faint from time to time, it's most likely due to vasovagal syncope. Most people who have episodes of vasovagal syncope lead normal lives. When fainting occurs frequently, however, it can disrupt your life.

If you have had vasovagal syncope—especially more than one episode—learning the things that trigger it and how to recognize warning symptoms can help you stop an episode or prevent future ones.

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Richard N. Fogoros, MD

By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.