Doctors sometimes refer to vasovagal syncope (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.

Other causes may include severe pain, exhaustion, or sudden changes in body posture. Some people have a predisposition to these episodes due to a health condition that affects blood pressure or the heart.

Although a person may sometimes sustain injuries as a result of passing out, VVS is generally harmless. However, a medical diagnosis is necessary to rule out more serious medical conditions.

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

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

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

People who experience these symptoms before fainting should lie down somewhere safe. 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.

A person who has fainted may feel tired, lightheaded, or nauseated when they come round.

Causes

VVS occurs when the nerves that regulate heart rate and blood vessel constriction temporarily lose some of their normal regulation.

Malfunctions generally occur when a stimulus, such as fear, or an abrupt change in body posture causes the blood vessels to widen suddenly. This widening leads to a sudden drop in blood pressure and a resulting lack of blood and oxygen to the brain. This lack of oxygen is what causes fainting.

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

• fear
• the sight of blood or gore
• getting blood drawn
• standing for a long time
• sudden changes in posture
• straining, such as during bowel movements
• severe pain
• intense exercise
• exposure to heat

What to do after fainting

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 may need to seek emergency medical attention after a fainting episode. Generally, medical care is only necessary for people who experience the following scenarios and symptoms:

• fainting while pregnant
• falling from a significant height
• sustaining a head injury or other severe injury
• loss of consciousness
• chest pain or difficulty breathing
• confusion, slurred speech, or issues with vision or hearing
• involuntary movements of the body

When to see a doctor

People who have previously experienced VVS should talk to their doctor if they experience any new triggers or symptoms.

People should also see a doctor if they experience fainting for the first time. However, it is not always possible to diagnose VVS from a single episode of fainting.

Some types of syncope can occur as a result of an underlying medical condition that requires treatment. Examples of such conditions include:

• diabetes
• heart disease
• Parkinson disease
• lung disease

Diagnosis

Typically, doctors will begin a diagnosis of VVS with a review of the person's medical history and any other symptoms. They will also conduct a physical examination. As part of this examination, the doctor will 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:

• Electrocardiogram (EKG), which measures electrical activity in the heart.
• Echocardiogram, which assesses heart motion and blood flow through the heart.
• Exercise stress test to evaluate heart function in response to exercise.
• Tilt-table test, in which the doctor will secure a 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.

Treatment

VVS does not typically require treatment. However, a person may sometimes be slow to regain consciousness after an episode of fainting. A bystander can intervene by laying the person on their back and raising their legs in the air. Doing this may help restore blood flow to the brain, thereby helping the person regain consciousness.

According to a 2016 review, there are limited treatment options for people with VVS. Doctors advise people with this condition to avoid known fainting triggers and take precautions to prevent injury when signs 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 adrenergic agonists: These drugs help raise blood pressure.
• Fludrocortisone: A type of corticosteroid that can help maintain blood pressure by increasing sodium and fluid levels in the body.
• Selective serotonin reuptake inhibitors (SSRIs): Antidepressant medications that may help moderate the nervous system response.

However, further studies are necessary to determine the effectiveness of these and other medical treatments for VVS.

Prevention tips

VVS is not always completely preventable. However, a person may be able to reduce the number of fainting episodes that they experience.

A person's doctor may provide the following recommendations for preventing VVS and the associated complications:

• identifying and avoiding situations that trigger fainting episodes
• engaging in moderate exercise
• drinking plenty of fluids to maintain blood volume
• consuming a diet that is higher in salt
• wearing compression stockings
• discontinuing medications that lower blood pressure
• immediately sitting or lying down when feeling faint

As with prescription medications, these preventive lifestyle approaches may work for some people and not others. Various factors, such as the person's blood pressure and heart function, may determine the effectiveness of these approaches.

Summary

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

Vasovagal syncope is usually not dangerous. However, people should seek medical attention if they faint when pregnant, experience additional symptoms, or fall and injure themselves when fainting. People should also see a doctor if they are unsure of the cause of fainting.

There are no standard treatments for vasovagal syncope. Instead, treatment generally involves making certain dietary and lifestyle changes, as well as avoiding potential triggers of fainting.