Vasovagal Syncope

Vasovagal syncope happens when your body's normal ability to control blood pressure doesn't work like it should, causing you to pass out. Vasovagal syncope is the most common type of reflex syncope, which happens automatically for reasons you can't control.


What is vasovagal syncope?

Vasovagal syncope (pronounced “vay-so-vay-gal sin-co-pee”) happens when your blood pressure and heart rate drop suddenly, causing you to pass out or faint.

Vasovagal syncope is the most common type of reflex syncope, which happens automatically for reasons you can't control. It’s also sometimes called neurocardiogenic syncope because it's caused by factors involving the heart, brain or both.

Who is at risk for vasovagal syncope?

One out of 3 people will experience vasovagal syncope at least once in their life, and it can happen to people of all age groups. In people under 40, vasovagal syncope causes about 85% of all passing out or fainting instances. In older adults, it makes up about half of those cases.

People with disorders that affect their autonomic nervous system, such as Parkinson's disease, are extremely unlikely to have vasovagal syncope. That's because their condition disrupts the normal functions of their nervous system.


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Possible Causes

What causes vasovagal syncope?

Vasovagal syncope is a reflex reaction to something happening around you, but the reflex is either too strong or happens at the wrong time. This all starts in your nervous system.

Part of your nervous system works without you having to think about it. This is called your autonomic (auto-nom-ick) nervous system, and it has two main subsystems:

  • This controls your “fight-or-flight” response. This is all about speed, reflexes, strength and preserving your safety. When your sympathetic nervous system is active, your heart rate and blood pressure go up and you are ready for quick action.
  • This controls your “rest-and-digest” response. It’s focused on nonemergency processes, including eating, digesting and other bodily functions. It's sometimes called the "feed-and-breed" response because it's also active during sexual arousal. One of the key nerves in this system is the vagus nerve, which controls your heart and blood pressure.

Under normal circumstances, these two systems balance each other out. That balancing act involves reflexes that your body develops. Think of these reflexes like a computer program that tells different systems in your body, “If this happens, then you should do this.”

If your vagus nerve becomes too active, it can cause your heart rate and blood pressure to drop too much or too fast (or both). If your blood pressure drops too much, this causes an “attack” of vasovagal syncope, and you pass out because there’s not enough blood flow to your brain.

What does it feel or look like to have vasovagal syncope?

Most of the time, vasovagal syncope happens when you’re standing or sitting. It's rare for it to occur if you’re lying down. It is common with specific triggers like having your blood drawn.

A brief period right before vasovagal syncope may happen where you’re most likely to have symptoms. This period is called prodrome (rhymes with "dome") and is less common in older adults. Recognizing prodrome for vasovagal syncope can be a vital tool to help avoid injury.

Common symptoms that happen about 30 to 60 seconds before an attack include:

Once an attack starts, the following are likely to happen:

  • Loss of consciousness and falling to the ground, usually for no more than 15 seconds.
  • Eyes remain open but roll up and back into your head.
  • Twitching movements, which can sometimes be mistaken for a seizure.
  • Loss of bladder control.
  • No interruption in breathing (which can happen with life-threatening conditions).

Once you come to, you’ll usually recover quickly (in about 20 to 30 seconds). Disorientation or confusion either doesn’t happen or they don’t last longer than 30 seconds. The following may also occur:

  • Anxiety or nervousness.
  • Dizziness.
  • Headache.
  • Nausea.
  • Pale skin.
  • Sweating.
  • Urge to use the bathroom.
  • Another attack of syncope, especially if you stand within 30 minutes of the first attack.


Common triggers that cause this condition

Vasovagal syncope is almost always triggered by something happening to you or around you. Common triggers include:

  • Needles or medical instruments. Vasovagal syncope is usually what causes people to faint when they have blood drawn or when they donate blood. Some people also pass out at the sight of certain medical tools or instruments, such as scalpels.
  • Seeing blood. Fainting at the sight of blood is also a common cause of vasovagal syncope.
  • Stress, anxiety or emotional upset. Strong emotions, especially overwhelming ones, can cause a person to pass out from vasovagal syncope.
  • Fatigue or exhaustion. Over-exertion, even just from standing too long, can be enough to cause a person to pass out.

Two main types of reflex syncope are similar to vasovagal syncope. The main difference is the causes are easier to identify.

  • Carotid sinus syndrome. This is more common in men over age 50. This reflex causes you to pass out when there is pressure on your neck. It can happen while shaving, wearing a tight collar or turning your neck a certain way.
  • Situational syncope. This group includes reflex syncope that's predictable and happens during certain activities or situations. A few examples of situational syncope are passing out when urinating, having a bowel movement, coughing, swallowing or after a meal.

Care and Treatment

What should I do after fainting unexpectedly?

If you faint unexpectedly, you should receive emergency medical care right away. Serious or life-threatening conditions can cause syncope. A healthcare provider should examine you right away to determine if a more severe condition caused you to faint.

It's also essential to get medical attention after fainting if you hit your head (even only slightly). People who are on blood-thinning medications should always get medical attention after a fall because they have a much higher risk for internal bleeding.


How serious is vasovagal syncope?

Vasovagal syncope is almost never a life-threatening condition on its own. That’s because it’s caused by a reflex your body is supposed to have. The reflex is just happening too strongly or at the wrong time.

However, passing out without warning can cause injury — either from falls or depending on what you’re doing at the time. It’s also important to remember that many serious or life-threatening conditions can also cause you to pass out. If you don't have a history of passing out, it's crucial to find out why you passed out or rule out a more serious problem.

How is vasovagal syncope diagnosed?

Your healthcare provider is likely also to ask questions about what might have caused your fainting. You should mention any recent changes in your health or unusual symptoms you’ve noticed, even ones that don’t seem important. These can help your provider accurately diagnose what caused you to faint.

Your healthcare provider may also run the following tests:

  • Blood tests. Several conditions that can cause fainting, such as low iron in your blood (anemia), can be detected by a blood test.
  • Electrocardiogram (EKG or ECG). This test measures electrical activity in your heart. It may help determine if you passed out because of a heart problem.
  • Electroencephalogram (EEG). This test measures electrical activity in your brain. This can help determine if you passed out because of a seizure — either caused by epilepsy or a heart problem.
  • Tilt-table test. This test has you lie on a table that’s then tilted upward. Patients with vasovagal syncope may pass out or start to pass out during this test.
  • Hemodynamic test. This test uses a tracer, which is a substance that is injected into your body. This tracer is visible on a special type of X-ray called a gamma camera and will allow your healthcare provider to see how your blood circulates. This can be especially helpful in finding problems that cause you to faint because your blood isn’t circulating correctly.

How is vasovagal syncope treated?

Most people who have vasovagal syncope will recover on their own, but some may need IV fluids (especially if they are dehydrated).

Other treatments that may be used include:

  • Medications: Some medications for heart rhythm disorders or blood pressure may help people with vasovagal syncope.
  • Pacing devices: In very rare cases, people with vasovagal syncope may need a pacemaker or other kind of implanted device that can help them avoid passing out because of pauses in their heartbeat.
  • Trigger education and avoidance: Knowing what causes your vasovagal syncope can help you avoid that trigger, or at least be ready for it. This knowledge can also help you act before you pass out, and you may be able to avoid passing out entirely.

What else can I do for my vasovagal syncope?

Many people who have vasovagal syncope can limit its impact on their lives, especially when they learn to recognize the symptoms of an attack. Your healthcare provider can help you learn more about the following:

Recognizing symptoms

Knowing what it feels like before you have an attack can allow you to sit or lay down so you're not hurt if you fall.

Anti-syncope techniques

If you can recognize an attack before it happens, you may be able to stop it. Your healthcare provider can teach you techniques that keep your blood pressure high enough so that you don’t pass out. These include:

  • Squeezing a foam or rubber ball. Clenching your fist like this may help you stay conscious.
  • Arm-tensing. Curl both of your hands like you’re holding something while wearing mittens. Then, with one hand facing palm-down and the other facing palm-up, hook your curled hands together. Once you have a good grip, try to pull your hands apart.
  • Leg-crossing. This technique is handy if you can't find a place to sit down. While standing, cross your legs so that one knee is behind the other. Make sure you can keep your balance and then tense up the muscles in your legs, belly and buttocks. This keeps blood higher up in your body, which can keep you from passing out.

Does vasovagal syncope ever go away?

It's very common for people to only have vasovagal syncope once in their lifetime. However, some people with specific triggers may have vasovagal syncope for the rest of their lives. For people who have repeated attacks of vasovagal syncope, your healthcare provider can tell you more about what to expect with it.

When To Call the Doctor

When should vasovagal syncope be treated by a healthcare provider?

You should talk to a healthcare provider if any of the following happen:

  • If you’ve never had vasovagal syncope before and pass out.
  • If you’ve never had vasovagal syncope before and have several instances where you’ve nearly passed out.
  • If you have been diagnosed with vasovagal syncope and your attack symptoms change or attacks become more frequent.

A note from Cleveland Clinic

Vasovagal syncope can disrupt your life and cause fear and anxiety. However, your healthcare provider can reassure you — and give you tips and resources. Their goal is to help you adapt to your condition, so you don’t have to stop living and enjoying your life.

Medically Reviewed

Last reviewed on 06/19/2022.

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