Vasovagal syncope (neurocardiogenic syncope) is the most common cause of fainting, or "passing out." It happens when your body reacts strongly to certain triggers, like a stressful event or the sight of blood.
Fainting causes you to lose consciousness temporarily. If you are standing when it occurs, you may fall down and become injured, so it's important to try to prevent future episodes.
Sometimes vasovagal syncope (or vasovagal response) 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.
What Are Symptoms of Vasovagal Syncope?
When you faint as a result of a vasovagal response, it can be sudden but sometimes you'll have warning signs a few seconds or minutes before. These signs are called the prodrome of syncope.
Symptoms that occur after you regain consciousness are called postdromal symptoms.
Prodromal symptoms of syncope can include:
- 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.
Vasovagal Episode Symptoms
Episodes of vasovagal syncope have several defining symptoms and 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 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.
What To Do If Someone Has Vasovagal Syncope
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.
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.
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 the warning signs of another fainting episode.
What Causes Vasovagal Syncope?
Vasovagal syncope occurs when something triggers the vasovagal reflex, which 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
- High levels of stress, anxiety, or fear
- 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.
Who’s at Risk for Vasovagal Syncope?
The reflex that causes vasovagal syncope can affect anyone. It is likely that most people will have a fainting episode sometime during their lives.
Young Adults and Adolescents
Vasovagal syncope can occur at any age but is more common in adolescents and young adults than in older people.
Prone to Recurrent Syncope
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
- Extreme fatigue
- Various aches and pains
When to See a Healthcare Provider
Contact your doctor if you experience your first-ever episode of syncope.
If you've already been diagnosed with vasovagal syncope, see your doctor if you are pregnant or have recurrent episodes.
Get medical attention right away if you other symptoms before you faint, such as:
- Blurred vision
- Chest pain
- 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. However, the exam is often helpful in identifying similar conditions, including:
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.
How Can You Prevent Vasovagal 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.
Vasovagal syncope is not life-threatening. However, injuries that result from falling may be dangerous. If episodes are frequent, this condition can significantly disrupt your life.
How Is Vasovagal Syncope Treated?
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.
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, and the ones that may help treat 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: 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.
- 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, 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're prone to syncope (fainting), avoid triggers such as:
- Excessive heat
- Stressful and intensely emotional situations
- Extreme pain
- Prolonged exercise or standing
Can certain foods impact vasovagal syncope symptoms?
Eating a diet 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 because it can have other, negative health effects.
Drinking more fluids may also help prevent fainting.
What are the after-effects of fainting?
After-effects of fainting can include:
- 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 you should avoid potentially dangerous situations, like driving.
Is vasovagal syncope a form of anxiety?
There's a strong link between vasovagal syncope and anxiety, and it can have a cyclical effect:
- Strong feelings of stress and anxiety may be a trigger for syncope.
- Recurrent syncope can increase anxiety and other mood disorders like depression.
Managing stress and anxiety may help prevent future vasovagal syncope.