Syncope: causes, symptoms, treatment, warning signs and tests

Syncope is the medical term for fainting or briefly passing out. It happens when there is a temporary reduction in blood flow to the brain, causing a person to lose consciousness and usually recover spontaneously within a short time.

Fainting can happen to an otherwise healthy person after prolonged standing, dehydration, emotional stress, pain or overheating. However, syncope can sometimes be the first sign of a heart rhythm problem, structural heart disease or another medical condition that needs investigation. This is why unexplained or recurrent fainting should not simply be ignored.

The important thing to remember is that syncope is a symptom, not a single disease. Finding out why someone fainted is the key to deciding whether treatment is necessary.

What happens during syncope?

The brain needs a continuous supply of oxygen-rich blood to function normally. If blood flow to the brain suddenly falls for a short period, a person may become lightheaded, lose awareness and collapse.

The drop in blood flow can occur because blood pressure falls, the heart rate becomes too slow or too fast, the heart cannot pump enough blood, or blood pools in the legs when a person stands.

Syncope is generally brief. Consciousness usually returns quickly once normal blood flow to the brain is restored. A person may nevertheless feel tired, weak, confused or unsteady for some time afterwards.

What are the three main causes of syncope?

Although there are several specific causes, syncope is commonly divided into three major groups:

1. Reflex or vasovagal syncope

This is the most common form of fainting. It occurs when the nervous system overreacts to a trigger, causing blood pressure and sometimes heart rate to fall suddenly.

Common triggers include:

• Emotional stress or fear
• Seeing blood
• Pain
• Having blood drawn
• Prolonged standing
• Heat
• Straining
• Certain bodily functions such as coughing or urination

Vasovagal syncope is generally considered benign, although a fall during an episode can cause injury.

2. Orthostatic syncope

Orthostatic or postural hypotension occurs when blood pressure drops significantly after moving from lying or sitting to standing.

It can be associated with:

• Dehydration
• Blood loss
• Certain medications
• Prolonged bed rest
• Conditions affecting the autonomic nervous system
• Low blood volume

A person may experience dizziness, blurred vision, weakness or fainting shortly after standing.

3. Cardiac syncope

Cardiac syncope occurs when a heart problem temporarily reduces blood flow to the brain.

Possible causes include:

• Abnormal heart rhythms
• Very slow heart rate
• Very fast heart rate
• Heart valve disease
• Structural heart disease
• Cardiomyopathy
• Other conditions that interfere with the heart’s ability to pump blood

Cardiac syncope deserves particular attention because some underlying heart conditions can be serious. Fainting during exercise, fainting while lying down, or fainting accompanied by palpitations or chest symptoms warrants prompt medical assessment.

What are the earliest signs of syncope?

Many people experience warning symptoms before actually fainting. Recognising these symptoms can sometimes prevent a fall.

The earliest signs may include:

• Lightheadedness
• Feeling weak or unsteady
• Nausea
• Feeling unusually warm
• Sweating or cold, clammy skin
• Blurred vision
• Seeing spots
• Tunnel vision
• Drowsiness
• Palpitations
• A feeling that you are about to pass out

These symptoms are particularly common with reflex or vasovagal syncope.

If these symptoms appear, sit or lie down immediately rather than trying to walk through them.

What are 5 symptoms of syncope?

Five common symptoms associated with syncope are:

1. Lightheadedness or dizziness
2. Blurred or tunnel vision
3. Nausea
4. Sweating or feeling unusually warm
5. Brief loss of consciousness or blacking out

Other symptoms can include weakness, headache, seeing spots, feeling groggy and feeling unsteady while standing.

What are the warning signs of syncope?

Warning signs can occur seconds or minutes before fainting. These include sudden dizziness, nausea, sweating, warmth, visual changes, weakness and a feeling of impending loss of consciousness.

However, not everyone gets a warning. Some forms of cardiac syncope can occur suddenly, leaving little time to sit or lie down.

This is one reason why unexplained fainting deserves proper evaluation, particularly when there are cardiovascular risk factors or concerning circumstances surrounding the episode.

What are the four stages of syncope?

There is no universally accepted medical classification of syncope into exactly four stages. However, for understanding what happens around a typical fainting episode, it can be useful to describe four phases:

1. Trigger phase: A trigger such as prolonged standing, heat, dehydration, pain or emotional stress may occur.

2. Pre-syncope phase: The person develops warning symptoms such as dizziness, nausea, sweating or tunnel vision.

3. Syncope phase: Blood flow to the brain falls sufficiently to cause a brief loss of consciousness and loss of postural tone.

4. Recovery phase: Blood flow returns towards normal and consciousness is regained. The person may initially feel tired, weak or confused.

Not every person experiences all four phases, and cardiac syncope may occur with little or no warning.

Is syncope a heart problem?

Syncope itself is not necessarily a heart problem.

Some fainting episodes are caused by reflex responses or orthostatic hypotension and occur in people without significant heart disease. However, syncope can also result from an abnormal heart rhythm, valve disease, cardiomyopathy or another cardiovascular condition.

This distinction is important. A person who faints after standing in a hot room and develops nausea and sweating may have a very different cause from someone who suddenly collapses while exercising.

Is syncope considered heart disease?

No. Syncope is not itself a type of heart disease.

It is a clinical symptom that can have cardiovascular, reflex, orthostatic and other causes. If testing reveals that fainting is caused by an arrhythmia or structural heart condition, then the underlying heart disease needs to be treated.

Is syncope a neurological disease?

Syncope is not, by itself, a neurological disease. The immediate mechanism is usually a temporary reduction in blood flow to the brain.

Neurological conditions can sometimes produce loss of consciousness or symptoms that resemble syncope. Seizures, for example, are different from syncope and require a different evaluation and treatment approach. Routine brain imaging or EEG is generally not recommended for every person with syncope when there are no focal neurological findings or other indications.

This is an important distinction because not every blackout is a seizure and not every blackout is syncope.

Is syncope a type of stroke?

No. Syncope is not a type of stroke.

A stroke occurs when blood flow to part of the brain is interrupted or when bleeding occurs in the brain. Syncope is a temporary loss of consciousness caused by a short-lived reduction in brain blood flow.

Although a person who has fainted may appear unresponsive, stroke and syncope are different medical conditions. Difficulty speaking, facial weakness, one-sided weakness or persistent neurological symptoms after an episode require emergency assessment.

Is syncope like a stroke?

Syncope and stroke can both involve sudden changes in consciousness or neurological function, but they are not the same condition.

A typical syncopal episode is brief, followed by spontaneous recovery. Stroke symptoms generally relate to damage to a particular area of the brain and may include weakness on one side, facial drooping, speech problems or other persistent neurological deficits.

If someone has fainted and does not recover normally, has difficulty speaking or moving, or develops other signs suggestive of stroke, emergency medical care is required.

Is syncope harmful?

Syncope may be harmless in some cases, but it should not automatically be considered harmless.

The risk depends largely on why the person fainted and what happened during the episode. Vasovagal fainting is usually not dangerous, but a person can sustain significant injuries from falling. On the other hand, fainting caused by certain heart rhythm problems or structural heart disease can be more serious.

A first unexplained episode, recurrent fainting or fainting associated with concerning symptoms deserves medical evaluation.

Who is most at risk for syncope?

Syncope can occur at any age. Certain groups, however, may have a higher risk of particular types of fainting.

Older adults are more vulnerable to syncope and its complications. Cardiac causes also become more important when a person has known heart disease, previous arrhythmias, structural heart disease or reduced heart function.

Vasovagal syncope is particularly common in children and young adults, although it can occur at any age. People who stand for long periods may also be more susceptible.

Can stress and anxiety cause syncope?

Yes, stress and anxiety can contribute to fainting in some people.

Strong emotions such as fear, distress or the sight of blood can trigger vasovagal syncope. The body’s response may cause heart rate and blood pressure to fall, temporarily reducing blood flow to the brain.

However, not every episode of fainting during a stressful situation should automatically be blamed on anxiety. A medical evaluation may still be appropriate, particularly if the episode is new, recurrent or associated with palpitations, chest pain or exercise.

How long can syncope last?

Syncope is usually brief. Consciousness commonly returns quickly once blood flow to the brain is restored. The person may continue to feel tired or unwell after waking up.

If someone remains unconscious for longer than expected, cannot be awakened, does not recover normally or is not breathing normally, the situation should be treated as an emergency rather than assumed to be ordinary syncope.

What tests are done for syncope?

The evaluation starts with a detailed medical history and physical examination. The doctor will want to know what the person was doing before fainting, whether there were warning symptoms, how long consciousness was lost and whether there were palpitations, chest pain or other symptoms. Blood pressure and heart rate may be checked in different positions.

Depending on the suspected cause, tests may include:

Electrocardiogram (ECG)

An ECG records the heart’s electrical activity and is an important part of the initial evaluation of syncope. It can provide clues to abnormal heart rhythms and other cardiac conditions.

Holter or ambulatory ECG monitoring

A Holter monitor records the heart rhythm continuously, often for 24 hours or longer. Longer event or patch monitors may be used when symptoms occur less frequently.

Echocardiogram

An echocardiogram uses ultrasound to examine the heart’s structure and function. It may be recommended when structural heart disease is suspected.

Blood tests

Blood tests may be used selectively to look for problems such as anaemia, metabolic abnormalities or other potential contributors. Routine comprehensive laboratory testing is not necessary for every patient.

Tilt-table test

A tilt-table test measures how heart rate and blood pressure respond when the body moves from a lying position towards an upright position. It can be particularly useful when reflex syncope or an orthostatic mechanism is suspected and the diagnosis remains uncertain.

Exercise stress test

An exercise stress test may be considered when fainting occurs during or around exercise or when an exercise-related heart rhythm problem needs to be investigated.

Electrophysiology study

An electrophysiology study may be used in selected patients when a significant heart rhythm abnormality is suspected. It allows specialists to examine the heart’s electrical activity in greater detail.

Neurological testing or brain imaging may be considered when the medical history or examination suggests a neurological cause, but these tests are not automatically required for every person who faints.

What kind of doctor treats syncope?

The right doctor depends on the suspected cause.

A general physician or internal medicine specialist can perform the initial assessment. If a cardiovascular cause is suspected, a cardiologist may investigate the heart rhythm and structure.

A neurologist may become involved when the history or examination suggests a neurological condition rather than typical syncope.

For recurrent or unexplained fainting, coordinated evaluation may involve more than one specialist.

What will a cardiologist do for syncope?

A cardiologist will generally try to determine whether the fainting could be related to the heart.

The evaluation may include:

• Detailed history of the episode
• Blood pressure and heart rate assessment
• Resting ECG
• Echocardiography when indicated
• Holter or longer-term rhythm monitoring
• Exercise testing in selected patients
• Tilt-table testing in appropriate cases
• Electrophysiology testing in selected patients

The exact tests depend on the patient’s age, medical history, symptoms and circumstances surrounding the fainting episode.

What is the proper treatment for syncope?

There is no single treatment for syncope because treatment depends on the underlying cause.

For reflex syncope, treatment may focus on recognising triggers, maintaining adequate hydration, avoiding prolonged standing and learning physical counter-pressure techniques when appropriate.

For orthostatic hypotension, treatment may involve addressing dehydration, reviewing medicines that lower blood pressure and treating the underlying condition. Some patients may need additional measures such as compression garments or medication.

When syncope is caused by a heart rhythm or structural heart problem, treatment is directed at that condition. Depending on the diagnosis, this may include medication, rhythm treatment or a cardiac device such as a pacemaker or implantable cardioverter-defibrillator.

What is the emergency treatment for syncope?

If someone suddenly faints:

1. Check whether they are breathing and responsive.
2. If they are breathing normally and there is no suspected injury, place them on their back and raise their legs if possible.
3. Do not make them stand up quickly.
4. Loosen tight clothing around the neck.
5. Once fully conscious, fluids may be offered when appropriate.
6. If the person is not breathing normally, begin CPR and call emergency medical services.
7. Seek emergency help if the person cannot be awakened within about one minute, does not recover normally, has chest pain, an irregular or pounding heartbeat, significant injury, seizure-like activity, difficulty speaking or moving, or fainted during exercise or while lying down.

A person who has fainted should not simply be told to “get up and walk it off.”

How to recover from syncope?

After fainting, stay lying down or seated until you feel completely stable. Getting up too quickly can cause another episode, particularly with vasovagal or orthostatic syncope.

Once fully alert, hydration may be helpful if dehydration contributed to the episode. However, recovery advice should be based on the underlying cause.

If you have never fainted before, faint repeatedly or have no obvious explanation for the episode, arrange a medical evaluation rather than assuming it was simply dehydration or stress.

What to do to avoid syncope?

Prevention depends on identifying the trigger or underlying condition. Helpful measures may include:

• Drink enough fluids when medically appropriate.
• Avoid standing still for prolonged periods.
• Rise slowly from lying or sitting.
• Avoid excessive heat.
• Recognise your personal warning symptoms.
• Sit or lie down immediately when you feel faint.
• Discuss medicines that may lower blood pressure with your doctor rather than stopping them yourself.
• Avoid known vasovagal triggers where possible.
• Follow treatment prescribed for any underlying heart or blood pressure condition.

If you experience warning symptoms while standing, crossing your legs or tightening the muscles of your legs and arms may help some people maintain blood pressure until they can sit or lie down.

When should you seek urgent medical attention?

Fainting requires particularly prompt evaluation when it:

• Happens during exercise
• Occurs while lying down
• Is accompanied by chest pain
• Is accompanied by significant palpitations
• Occurs in someone with known heart disease
• Happens repeatedly without an explanation
• Causes a serious injury
• Is followed by persistent confusion
• Is associated with difficulty speaking or moving
• Occurs with seizure-like activity
• Does not resolve normally

These features can indicate a potentially serious underlying condition and should not be dismissed as ordinary fainting.

Syncope vs fainting: is there a difference?

In everyday language, fainting, passing out and blacking out are often used interchangeably.

Syncope is the medical term for a specific type of temporary loss of consciousness associated with a temporary reduction in brain blood flow and usually rapid spontaneous recovery. Not every episode of loss of consciousness is necessarily syncope; seizures and other conditions can produce similar-looking episodes.

That distinction matters because the investigation and treatment can be completely different.

Frequently asked questions about syncope

What is the main cause of syncope?

There is no single cause. Reflex or vasovagal syncope is the most common type, while orthostatic hypotension and cardiac conditions are other important causes.

Is syncope harmful?

Often, syncope itself is brief and not dangerous, particularly when caused by vasovagal mechanisms. However, falls can cause injury, and syncope caused by serious heart conditions can be dangerous.

Is syncope a heart problem?

Not always. Syncope can be caused by reflex mechanisms or blood pressure changes, but it can also result from heart rhythm or structural heart problems.

Can stress and anxiety cause syncope?

Yes. Strong emotional stress, fear or distress can trigger vasovagal syncope in susceptible people.

How long can syncope last?

Loss of consciousness is generally brief, with recovery usually occurring quickly. Persistent unconsciousness or failure to recover normally requires emergency assessment.

What tests are done for syncope?

Depending on the suspected cause, evaluation may include an ECG, blood pressure measurements, blood tests, Holter monitoring, echocardiography, exercise testing, tilt-table testing and, in selected cases, electrophysiology or neurological testing.

What doctor should I see for syncope?

A general physician or internal medicine specialist can start the evaluation. A cardiologist is particularly important when a heart-related cause is suspected, while a neurologist may be involved when neurological symptoms suggest an alternative diagnosis.

Is syncope like a stroke?

No. Syncope and stroke are different conditions. Stroke causes brain injury due to interrupted or bleeding blood vessels, whereas syncope involves a temporary reduction in brain blood flow followed by recovery.

What should I do if I feel like I am about to faint?

Sit or lie down immediately, preferably with your legs raised if possible. Do not attempt to continue walking or standing.

Final thoughts

Syncope may be caused by something relatively simple, such as dehydration, prolonged standing or a vasovagal reaction. But fainting can also be associated with an abnormal heart rhythm or another condition that requires treatment.

The most useful question after a fainting episode is therefore not simply “Why did I faint?”, but “What caused the temporary reduction in blood flow to my brain?”

A careful medical history, physical examination and appropriate testing can help answer that question. An ECG is an important part of the initial assessment, while tests such as Holter monitoring, echocardiography, tilt-table testing or exercise testing are selected according to the suspected cause.

If fainting is new, recurrent, unexplained or associated with chest pain, palpitations, exercise or neurological symptoms, seek medical attention promptly.

Medical disclaimer

This article is intended for general health education and should not replace an examination or diagnosis by a qualified healthcare professional. Anyone who experiences unexplained loss of consciousness should discuss it with a healthcare provider, particularly if the episode is recurrent or associated with warning signs of a serious condition.