Syncope, commonly called fainting, is a temporary loss of consciousness caused by a brief decrease in blood flow to the brain. It usually occurs suddenly, lasts a short time, and is followed by a spontaneous and complete recovery.

Some people experience presyncope, meaning they feel as though they are about to faint but do not completely lose consciousness.

Before losing consciousness, you may experience:
 

• Lightheadedness or dizziness

• Weakness

• Blurred, dim, or tunnel vision

• Nausea

• Feeling hot or flushed

• Sweating

• Pale skin

• Ringing in the ears

• Heart racing or pounding

• A feeling that you are about to pass out

Some episodes, particularly those caused by abnormal heart rhythms, may occur without any warning symptoms.

Common Causes
 

Vasovagal Syncope
 

Vasovagal syncope is the most common type of fainting. It occurs when the nervous system suddenly causes the heart rate and/or blood pressure to fall, temporarily reducing blood flow to the brain.

Common triggers include:
 

• Prolonged standing

• Heat

• Pain

• Emotional distress

• Fear

• Seeing blood

• Blood draws or medical procedures

• Dehydration

• Straining during a bowel movement

• Coughing or urinating in some people

People often experience nausea, warmth, sweating, or lightheadedness before fainting.

Orthostatic Hypotension
 

Orthostatic hypotension is a significant decrease in blood pressure after standing.

Possible causes include:
 

• Dehydration

• Blood loss

• Prolonged bed rest

• Certain medications

• Autonomic nervous system disorders

• Older age

Medications that lower blood pressure, increase urination, or affect the nervous system may contribute.

Heart-Related Syncope
 

Some episodes of fainting are caused by problems with the heart and require further evaluation.

Possible causes include:
 

• Abnormally fast or slow heart rhythms

• Heart block

• Structural heart disease

• Cardiomyopathy

• Severe heart valve disease

• Certain inherited electrical disorders of the heart

Heart-related syncope is particularly concerning when fainting occurs during exercise, while lying down, without warning, or in someone with known heart disease.

Other Conditions That Can Resemble Syncope
 

Not every episode of loss of consciousness is true syncope. Other possibilities include:

• Seizures

• Low blood sugar

• Medication or substance effects

• Certain neurological conditions

• Psychogenic/functional episodes

A detailed description of what happened before, during, and after the event can help determine the cause.

How Is Syncope Evaluated?
 

-Evaluation begins with a detailed medical history and physical examination.

Your healthcare provider may ask about:
 

• What you were doing when the episode occurred

• Whether you were standing, sitting, lying down, or exercising

• Symptoms immediately before fainting

• How long you were unconscious

• Symptoms after waking

• Previous episodes

• Current medications

• Heart or neurological conditions

• Family history of heart disease or sudden unexplained death

-Blood Pressure and Heart Rate may be measured while lying down and again after standing to look for orthostatic hypotension.

-Electrocardiogram (EKG/ECG) evaluates the electrical activity of the heart and may identify abnormal rhythms or other findings suggesting a cardiac cause.

-Additional testing is based on the suspected cause and may include:
 

• Blood tests

• Blood glucose testing

• Heart rhythm monitoring

• Echocardiogram

• Exercise testing

• Tilt-table testing

• Specialist evaluation

-Brain imaging, EEGs, and other neurological testing are not routinely necessary for uncomplicated syncope unless the history or examination suggests a neurological cause.

When Fainting May Be More Concerning
 

Further evaluation is particularly important when fainting:
 

• Occurs during exercise

• Occurs while lying down

• Happens suddenly without warning

• Is associated with chest pain

• Is associated with significant shortness of breath

• Is associated with persistent or severe palpitations

• Occurs in someone with known heart disease

• Occurs repeatedly without an identified explanation

• Is associated with an abnormal EKG

• Occurs in someone with a family history of sudden unexplained or premature cardiac death

• Causes a significant injury

When to Call 911
 

Seek emergency medical attention if fainting is accompanied by:
 

• Chest pain or pressure

• Severe difficulty breathing

• Signs of a stroke, such as facial drooping, weakness, difficulty speaking, or sudden severe neurological symptoms

• A sustained rapid or irregular heartbeat

• Failure to quickly regain consciousness

• Persistent confusion or significant neurological symptoms after awakening

• Severe bleeding

• A serious injury from the fall

Fainting during exercise or fainting in someone with significant known heart disease also warrants prompt medical evaluation.

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Preventing Future Episodes
 

Prevention depends on the cause. Recommendations may include:
 

• Staying adequately hydrated

• Avoiding prolonged standing when possible

• Rising slowly from bed or a chair

• Recognizing early warning symptoms

• Reviewing medications that may lower blood pressure

• Avoiding known triggers

• Treating an underlying heart rhythm or cardiovascular condition when present

Repeated or unexplained fainting should not simply be assumed to be harmless. Identifying the cause is important, particularly when features suggest a possible cardiac cause.