Vasovagal syncope (VVS) describes fainting that occurs in response to a sudden drop in heart rate or blood pressure.

Doctors sometimes refer to VVS as neurocardiogenic syncope or reflex syncope. This condition typically occurs when the body overreacts to a stimulus that induces a state of fear or emotional distress.

Although a person may sometimes sustain injuries because of passing out, VVS does not usually require treatment. However, a diagnosis is necessary to rule out more serious medical conditions.

In this article, we outline some common causes and symptoms of VVS. We also cover the treatment options available and provide tips on how to prevent fainting episodes.

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VVS occurs when the part of the nervous system responsible for regulating heart rate and blood vessel constriction temporarily loses control of this regulation.

People may experience VVS for several reasons. Some common triggers include:


Anxiety and other related conditions, such as depression, can exacerbate VVS, resulting in cyclical events of distress and fainting. Furthermore, people who experience VVS in response to psychological distress tend to have a lower quality of life than those who do not.

Consequently, in these cases, a more holistic approach to treatment that addresses a person’s psychological well-being in addition to VVS is more effective than treating VVS alone.

Sight of blood and gore

A phobia of blood and gore accounts for 3-4% of all phobias. When people with this phobia see blood, be it in real life or in a movie, their heart rate increases for a short interval and then dramatically drops, which often results in fainting.

As the sight of blood promotes such high levels of fear and disgust, it is not unusual for people with this phobia to decline necessary medical treatment, especially if it involves injections or blood withdrawal.

Standing or sitting upright

Orthostatic hypotension, also known as postural hypotension, is a form of low blood pressure that occurs when a person goes from lying down to sitting or standing up. Before a person faints, they may feel lightheaded and dizzy. However, some people may experience no symptoms and faint without warning.

In many cases, researchers do not know exactly what triggers a person’s blood pressure to drop excessively when standing or sitting up, but some causes could include:

  • diuretics, which are drugs that increase urination
  • vasodilators, which are drugs that lower blood pressure
  • antipsychotic or antidepressant medication
  • autonomic nervous system dysfunction
  • chronic bleeding
  • heart problems

Bowel movements

If someone is experiencing severe constipation, they may faint when passing a stool due to increased pressure in the rectum. When the pressure in the rectum increases, the epiglottis — a piece of tissue that sits behind the tongue at the back of the throat — closes over the windpipe and causes the diaphragm to tighten excessively.

This series of physiological responses stimulates the parasympathetic nervous system, which causes a rapid drop in blood pressure and a reduction in blood flow to the brain. When the brain no longer receives a healthy amount of oxygen, a person loses consciousness and faints.

Intense heat

When a person is in a hot environment, and their core temperature is reaching a dangerous level, the body will divert blood to the surface of the skin to cool itself down and prevent overheating. However, in combination with dehydration, this response can lead to a sudden and significant drop in blood pressure, causing a person to faint.


Exercise-induced VVS is rare, and doctors must rule out other life threatening diseases, including heart disease and arrhythmia, before confirming a diagnosis.

Researchers are not sure what causes VVS during exercise, but they think that the Bezold-Jarisch reflex — a type of inhibitory reflex that lowers blood pressure — could be responsible.

Additionally, changes in serotonin, peripheral opioids, and adenosine levels may trigger VVS when a person is engaging in high levels of physical exertion.

VVS does not typically require treatment. However, a bystander can intervene by laying the person on their back and raising their legs in the air. These actions may help restore blood flow to the brain, thereby helping the person regain consciousness more quickly.

According to a 2016 review, limited treatment options are available for people with VVS. Doctors advise people with this condition to avoid known fainting triggers and take precautions to prevent injury when symptoms of imminent fainting begin.


Medications are not usually necessary for VVS. However, in some circumstances, the following medications may be effective in reducing the frequency of VVS episodes:

  • Alpha-1 agonists: These drugs help raise blood pressure.
  • Fludrocortisone: This drug is a type of corticosteroid that can help maintain blood pressure by increasing sodium and fluid levels in the body.
  • Beta-blockers: These drugs are more effective in preventing VVS in people who are older than 42 years. However, more research is necessary to determine the risk of orthostatic hypotension.

Researchers need to complete more studies to determine the effectiveness of these and other medical treatments for VVS.

Lifestyle changes

VVS is not always completely preventable. However, a person may be able to reduce the number of fainting episodes that they experience by making certain lifestyle adjustments. These include:

  • avoiding situations that trigger fainting episodes
  • engaging in moderate exercise
  • drinking plenty of fluids to maintain blood volume
  • increasing salt intake
  • wearing compression stockings
  • discontinuing medications that lower blood pressure
  • sitting or lying down immediately when feeling faint

Some people who experience VVS do not notice any warning signs before fainting. Others may have symptoms such as:

  • weakness
  • gray or pale appearance
  • feeling of warmth
  • sweaty or clammy skin
  • lightheadedness
  • dizziness
  • blurred vision

People who experience these symptoms before fainting should lie down in a safe place. Lying down will help the body maintain adequate blood flow to the brain, which may prevent fainting. It will also minimize the risk of a fall or injury in the event of fainting.

After fainting, a person may feel tired, lightheaded, or nauseated.

A person who has experienced VVS may feel tired, weak, and nauseated when they come round. It is important that they rest before getting up and continuing with their day.

In some cases, people should seek emergency medical attention after a fainting episode, especially if they have additional symptoms that overlap with signs of a heart attack.

People who have previously experienced VVS should contact a doctor if they experience any new triggers or symptoms. Some types of syncope can occur as a result of an underlying medical condition that requires treatment. Examples of such conditions include:

Typically, doctors will begin a diagnosis of VVS by reviewing the person’s medical history. They will also conduct a physical examination and take blood pressure readings while the person is standing, sitting, and lying down.

A doctor may also attempt to rule out alternative causes of fainting using one or more tests. Examples of such tests include:

  • Blood tests: A doctor may use these to rule out any underlying health conditions that present with fainting.
  • Electrocardiogram (EKG): An EKG measures electrical activity in the heart.
  • Echocardiogram: This test assesses heart motion and blood flow through the heart.
  • Exercise stress test: This test evaluates heart function in response to exercise.
  • Tilt-table test: For this procedure, the doctor will secure the person to a padded table that tilts at different angles. Various monitors detect and record heart activity, blood pressure, and oxygen levels while the table positions the person at different angles.

Vasovagal syncope refers to fainting that occurs in response to a sudden drop in heart rate or blood pressure.

VVS is usually not dangerous. However, people should seek medical attention if they faint with additional symptoms or fall and injure themselves during an episode. People should also see a doctor if they are unsure of the cause of fainting.

There are no standard treatments for VVS. Instead, doctors tend to recommend dietary and lifestyle adjustments to prevent fainting.