What Is Vasovagal Syncope? Causes, Symptoms, and Treatments

Key takeaways:

Vasovagal syncope is a common condition where you may faint under certain circumstances. This can happen when the vagus nerve is overstimulated.
Vasovagal symptoms include dizziness, lightheadedness, nausea, and sweating. Severe cases may cause syncope, or loss of consciousness.
Pain, nausea, fear, and straining for a bowel movement are common causes of vasovagal syncope.
Vasovagal syncope can usually be managed with good hydration, squeezing the legs together, and lying down when symptoms start.

Have you ever felt a little queasy at the sight of blood? Or gotten dizzy and clammy when you hit your funny bone? Perhaps you’ve even passed out after vomiting. If this sounds familiar, you may have experienced a vasovagal reaction.

Vasovagal syncope is a common condition that occurs when the body’s automatic nervous system briefly overreacts. It happens to about half of all people at some point in their lives.

Most of the time, vasovagal syncope is just a nuisance. But, for some people, it can lead to serious falls and injuries. Knowing the triggers for vasovagal syncope is the first step to managing the condition.

What is vasovagal syncope?

In vasovagal syncope, the vagus nerve — a major nerve that helps to regulate heart rate and blood pressure — becomes overly stimulated. When this happens, the heart rate slows and blood vessels relax, causing a sudden drop in blood pressure. This drop reduces blood flow to the brain, which can lead to syncope, or a brief loss of consciousness or fainting.

What causes vasovagal syncope?

Vasovagal syncope happens when your vagus nerve overreacts or gets overstimulated. This causes your heart rate and blood pressure to drop so low that blood flow to the brain is reduced.

The vagus nerve travels from behind the brain, through the neck, to organs in the chest and abdomen. The vagus nerve is part of the fight-flight-freeze response, and generally it has a calming effect. It belongs to the parasympathetic nervous system, and it helps to:

Slow your heart rate.
Lower your blood pressure.
Control your rate of breathing.
Allow normal movement of the digestive tract.

Problems happen when the vagus nerve has an outsized response to a trigger, which can lead to a quick drop in your heart rate, blood pressure, and blood flow to your brain.

Things that can bring on vasovagal syncope include:

Severe emotional stress
Pain
Disturbing images
The sight of blood
Nausea and vomiting
Long periods of standing, especially in hot environments
Straining for a bowel movement
Urination, especially in the middle of the night (also known as “micturition syncope”)
Heavy coughing

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Dehydration will often make the symptoms worse. For example, someone with diarrhea from a stomach flu or food poisoning may be more susceptible to a vasovagal reaction.

Why do people get vasovagal syncope?

Although vasovagal syncope is very common, experts aren’t clear on why some people get it and others don’t. In some cases, especially for men, the problem may be genetic. So, if you come from a family of fainters, it’s important to avoid things that might trigger an episode.

So far, there’s no cure for vasovagal syncope.

What are vasovagal syncope symptoms?

Vasovagal syncope refers to the loss of consciousness (fainting) that happens with vasovagal symptoms. These symptoms can include:

Lightheadedness
Nausea
Tunnel vision
Ringing in the ears
Sweating and clamminess

It’s important to recognize the symptoms of vasovagal syncope before they become severe. If your episodes are difficult to manage, you’ll likely be referred to a cardiologist, a healthcare professional who specializes in heart conditions.

Does a vasovagal reaction always result in fainting?

Most of the time, vasovagal symptoms won’t cause you to faint. But you may feel weak, nauseated, and clammy. Usually, you’ll have time to get yourself into a safer position before the symptoms become severe.

Lying down and propping your feet up above the level of the heart will often make you feel better within a few minutes. This simple action helps blood flow back to the brain, which counteracts the effects of low blood pressure. It’ll also keep you from falling and hurting yourself.

If your case is more severe, you may pass out suddenly and without warning. This can be dangerous. You could break a bone or experience a concussion from a hard fall, if you aren’t able to sit or lie down before losing consciousness.

How is vasovagal syncope diagnosed?

To make a diagnosis, a healthcare professional will ask about any supplements, over-the-counter (OTC) medications, or prescription medications that you’re taking. That way, they can be sure that none of these medications are causing trouble for you.

Initial testing may include:

A physical exam
An electrocardiogram (ECG or EKG)
Blood work
Exercise stress testing with EKG

Depending on what this first round of tests finds, your healthcare team may order more tests. You might need an echocardiogram, which can show the heart’s strength and be used to check the valves and look for heart damage.

You may also be asked to wear a heart rhythm monitor. This device records your heart rhythm to check for unusual skips or pauses that might cause you to faint.

What is the treatment for vasovagal syncope?

In most cases, there’s no specific vasovagal syncope treatment. A healthcare professional will recommend that you stay well hydrated and avoid the things that can trigger an episode.

Here are some ways to treat or reduce the risk of vasovagal syncope:

Hydration and electrolyte balance: Make sure you’re getting enough water and salt every day.
Yoga: Regularly practicing yoga may help lower your risk of vasovagal syncope. But avoid hot yoga.
Medications: People with heart rhythm or blood pressure problems may need to take medications, like beta blockers, midodrine, mineralocorticoids, and selective serotonin reuptake inhibitors (SSRIs).
Pacemaker: If you have a low heart rate due to a heart condition — like heart block or heart failure — then you may benefit from a pacemaker. This is a small device that a healthcare professional implants under your skin to help control your heart beat.

How to prevent vasovagal syncope?

You may be able to avoid a fainting episode if you’re able to recognize the signs and symptoms and take action. If you’re feeling lightheaded or dizzy, these strategies may lessen your chances of fainting of falling down:

Sit or lie down.
Cross your legs and tense the muscles of your legs, abdomen, and glutes.
Tense your arms and make fists with your hands.

These techniques can help keep your blood pressure high enough to avoid fainting.

When should you see a doctor for a vasovagal reaction?

If you faint, it's a good idea to get a medical checkup. This is especially true if the episode happens without warning, while driving, or causes a fall or injury.

Vasovagal syncope itself isn’t always serious. But it’s important to rule out more serious health issues that could cause fainting. These include problems with heart muscle strength or rhythm, or even neurological conditions, like seizures.

Frequently asked questions

Vasovagal syncope is usually harmless. But it can lead to injuries from a fall. In rare cases, a heart condition can cause vasovagal syncope. And this heart condition could be deadly if left untreated.

Vasovagal episodes can last anywhere from a few seconds to a couple of minutes. As soon as a person falls to the floor, their blood pressure increases to normal levels quickly. However, it may take a few minutes to fully restore normal blood flow. So, it’s important to take it easy after a vasovagal episode.

Yes, most people will have only one episode of vasovagal syncope. But about 35% of people will continue having episodes throughout their life.

The bottom line

Vasovagal syncope is a common problem that many people experience at some point. In most cases, you can keep yourself safe by staying hydrated, avoiding triggers, and sitting or lying down if symptoms occur. For some people, a regular yoga practice can help manage the condition. If you experience vasovagal symptoms frequently or without warning — or if you fall and get injured due to these symptoms — be sure to seek help from your primary care provider.

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Written by:

Sarah A. Samaan, MD

Sarah Samaan, MD, FACC, FACP, FASE is a board-certified cardiologist who practiced clinical cardiology for nearly 30 years. She is a member of the American College of Cardiology and the American College of Physicians, among others.

Edited by:

Alex Eastman, PhD, RN

Alex Eastman, PhD, RN, is a California-based registered nurse and staff medical editor at GoodRx, where he focuses on clinical updates and Latino health.

Reviewed by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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