What Is Vasovagal Syncope?

The Most Common Cause of Fainting

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Vasovagal syncope (or neurocardiogenic syncope) is the most common cause of fainting, or "passing out."

Fainting causes you to lose consciousness temporarily. If you are standing when it occurs, you may fall down and become injured, so it is important to try to prevent future episodes. Sometimes vasovagal syncope can be a sign of an underlying medical problem.

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

vasovagal syncope
Verywell / Brooke Pelczynski

Vasovagal Syncope Symptoms

When you faint as a result of a vasovagal response, it can be quite sudden. Sometimes, you will have warning signs a few seconds or a few minutes before you faint. These signs are sometimes referred to as a prodrome of syncope. Symptoms that occur 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

Prodromal symptoms may be followed by a sensation of "graying out," in which colors and light become dim. This is followed by a loss of consciousness. The time between the onset of prodromal symptoms and actually passing out can range from a few minutes to just a second or two.

If you feel like you’re going to faint, you may be able to stop the episode 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 stand up.

Syncope Characteristics

Episodes of vasovagal syncope have several defining features:

  • They almost always occur while 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.
  • People who have vasovagal syncope 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.
  • If someone tries to hold you up during a vasovagal episode, being in the standing position can prolong the time you are unconscious.

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 and call for professional medical help.

Postdromal Symptoms

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

It is important to note that until these symptoms disappear, you are at risk of fainting again. Therefore, you will need to avoid driving, climbing ladders, or doing anything that could be dangerous if you faint again. You should also be aware of warning signs of another fainting episode.

Recurrent Syncope

People who have had one or two episodes of vasovagal syncope often learn to recognize the warning signs. You can usually prevent an episode by lying down and elevating your legs.

On the other hand, trying to "fight off" an episode of vasovagal syncope by forcing yourself to remain standing or sitting up and "willing yourself" not to faint almost never works.

Older people with vasovagal syncope are more likely to have atypical syncope. This means there are no clear triggers and no warning signs.

In general, vasovagal syncope is not life-threatening, but injuries that result from falling may be dangerous. If episodes are frequent, this condition can significantly disrupt your life.

When to See a Healthcare Provider

You should contact your doctor if you experience your first-ever episode of syncope. If you have already been diagnosed with vasovagal syncope, you should see your doctor if you are pregnant or have recurrent episodes. If you have symptoms such as blurred vision, chest pain, confusion, trouble talking, shortness of breath, or irregular heartbeat before you faint, you should get medical attention right away.

Causes of Vasovagal Syncope

Vasovagal syncope occurs when something triggers the vasovagal reflex. This causes blood vessels to dilate (widen) suddenly. Dilation of the blood vessels causes a significant amount of the blood in the body to pool in the legs.

This pooling is often accompanied by a slowing heart rate. As a result, the blood pressure will suddenly drop. If the drop in blood pressure is enough to rob the brain of the amount of oxygen it needs, fainting occurs.

Common triggers of vasovagal syncope include:

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

Vasovagal syncope is more likely to occur when a person is dehydrated. Causes of dehydration can include a viral illness, vigorous exercise, or sleeping through the night without drinking water.

Risk Factors

The reflex that causes vasovagal syncope can affect anyone. It is likely that most people will have a fainting episode sometime during their lives.

Vasovagal syncope can occur at any age, but it is much more common in adolescents and young adults than in older people.

Some people are particularly prone to vasovagal episodes and may faint even with relatively mild triggering events. These people tend to have recurrent episodes of syncope, beginning in adolescence. They will often have several different kinds of triggers.

Rarely, some people have frequent vasovagal syncope that is so difficult to treat that they become virtually disabled by it. This can be associated with a form of dysautonomia, an imbalance of the autonomic nervous system. The autonomic nervous system is the part of the nervous system that controls things like our heartbeat and breathing.

Dysautonomia makes a person very prone to the vasovagal reflex that causes syncope. It's often accompanied by other symptoms of the dysautonomias, such as abdominal bloating or cramps, diarrhea, constipation, extreme fatigue, and various aches and pains.


Vasovagal syncope is caused by the vasovagal reflex, which makes blood pressure drop. Triggers of the reflex can include pain, emotional distress, and overheating. Fainting episodes are more common in adolescents and young adults, and ome people are especially prone to them.

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 examination of people with vasovagal syncope is usually completely normal. However, the exam is often helpful in identifying similar conditions, including orthostatic hypotension or postural orthostatic tachycardia syndrome (POTS).

With orthostatic hypotension, your blood pressure falls when you stand up, and you may feel dizzy or lightheaded. POTS is a condition in which a person becomes lightheaded and also has heart palpitations (irregular beats) when they stand up.

Sometimes tests are needed to diagnose vasovagal syncope. For example, you might need to have a tilt table study.

In this test, you are strapped to a table that tilts upward to put you in a position similar to standing. This allows the doctor to measure your heart rate and other factors that may be responsible for fainting episodes. A tilt table study can help distinguish vasovagal syncope from orthostatic hypotension.

Is There Treatment for Vasovagal Syncope?

People who have a single, one-time episode of vasovagal syncope generally do not need any medical treatment at all. But if you have had recurrent episodes, you are likely to have even more episodes unless you are treated.

As anyone with vasovagal syncope knows, these fainting episodes can come at the most inconvenient or impractical times and can greatly disrupt your life. Fortunately, treatment is usually helpful. There are two main types of therapy for vasovagal syncope: medication and exercise.


Medications can help regulate blood pressure and heart rate. Those that have been shown to be of some help in the treatment of vasovagal syncope include:

  • Midodrine, a drug that causes narrowing (constriction) of the blood vessels
  • Norpace (disopyramide), an antiarrhythmic drug that regulates your heartbeat
  • Selective serotonin reuptake inhibitors (a type of antidepressant)
  • Theophylline, which is typically used to treat asthma


Some people have been able to stop an episode of vasovagal syncope by immediately doing exercises that tense the muscles. These exercises can reduce blood vessel dilation and increase the amount of blood being returned to the heart.

Examples 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, be sure to meet with your healthcare provider before starting a fitness plan. You may need to undergo stress testing and other exams to determine how much exercise you can do safely.

Pacemakers (a device that regulates the heartbeat) were once thought to be helpful in people with vasovagal syncope. This is no longer thought to be true.


Vasovagal syncope is the main cause of fainting. It occurs when someone is upright and their blood pressure drops. This causes them to lose consciousness temporarily. Sometimes, fainting is a one-time event. For other people, it may happen frequently.

Things that can trigger an episode of vasovagal syncope include having your blood drawn or an emotionally upsetting event. When diagnosed properly, the condition can usually be managed with medications and/or certain exercises.

A Word From Verywell

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—you should learn as much as you can about this condition. Learning the things that trigger it and how to recognize warning symptoms can help you stop an episode or prevent future ones.

Frequently Asked Questions

  • Is there anything I can do to prevent vasovagal syncope?

    If you know you are prone to syncope (fainting), avoid possible triggers such as excessive heat, stressful and intensely emotional situations, dehydration, extreme pain, and prolonged exercise or standing.

    There are other potential triggers that differ between people. A doctor can examine your medical history and give you specific prevention tips.

  • Can certain foods impact vasovagal syncope symptoms?

    Eating a diet that is slightly higher in salt may help prevent syncope symptoms by keeping blood pressure up. Check with your doctor before adding extra salt to your diet, however, because it can have other, negative health effects. Drinking more fluids may also help prevent fainting.

  • What are the aftereffects of fainting?

    Aftereffects of fainting can include nausea, dizziness, fatigue, and appetite loss. These can last from a few hours to multiple days. Fainting again is more likely while these symptoms are present, which is why potentially dangerous situations should be avoided, such as driving a vehicle.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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