Fainting, "blacking out", or syncope is the temporary loss of consciousness followed by the return to full wakefulness. This loss of consciousness may be accompanied by loss of muscle tone that can result in falling or slumping over. To better understand why fainting can occur; it is helpful to explain why somebody is awake.


The brain has multiple parts, including two hemispheres, thecerebellum, and the brain stem. The brain requires blood flow to provide oxygen and glucose (sugar) to its cells to sustain life. For the body to be awake, an area known as the reticular activating system located in the brain stem needs to be turned on, and at least one brain hemisphere needs to be functioning.


For fainting or syncope to occur, either the reticular activating system needs to lose its blood supply, or both hemispheres of the brain need to be deprived of blood, oxygen, or glucose. If blood sugar levels are normal blood flow must be briefly disrupted to the whole brain or to the reticular activating system.


Fainting is not caused by head trauma, since loss of consciousness after a head injuryis considered a concussion. However, fainting can cause injury if the person falls and hurts themselves, or if the faint occurs while participating in an activity like driving a car.


Unconsciousness is an obvious sign of fainting.


Vasovagal syncope


  • Before fainting, you may feel light-headed and shaky and experience blurred vision.
  • You may "see spots in front of your eyes".
  • During this time, observers note paleness, dilated pupils, and sweating.
  • While unconscious, you may have lowpulse rate (less than 60 beats/minute).
  • You should quickly regain consciousness.


Situational syncope


  • Consciousness returns when the situation is over, usually very quickly.


Postural syncope


  • You may have noted a blood loss (black stools, heavy menstrual periods) or fluid loss (vomiting, diarrhea, fever).
  • You may have experienced light-headedness when sitting or standing.
  • Observers may note paleness, sweating, or signs of dehydration (dry lips and tongue).


Cardiac syncope


  • You may report palpitations (awareness of pounding, fast, or abnormal heartbeat), chest pain, or shortness of breath.
  • Observers may note a weak, abnormal pulse, paleness, or sweating.
  • Syncope often occurs without warning or following exertion.


Neurologic syncope


  • You may have headache, loss of balance, slurred speech, double vision, or vertigo (a feeling that the room is spinning).
  • Observers note a strong pulse during the unconscious period and normal skin color.




People experiencing a seizure may report strange sensations that precede the unconscious period (this is referred to as an aura):

  • Incontinence (inability to hold urine or stool) is common.
  • If observers are present during the seizure, they note sustained convulsions (lasting longer than 8 seconds).
  • A prolonged period of confusion, lasting several minutes, follows the seizure.
  • During a seizure, people often scrape themselves or bite their tongues.


Fainting has many different causes.


Vasovagal syncope: Also known as the "common faint", this is the most frequent cause of syncope. It results from an abnormal circulatory reflex.


The heart pumps more forcefully and the blood vessels relax, but the heart rate does not compensate fast enough to maintain blood flow. People older than 45 years rarely experience a first "common faint".


Causes of vasovagal syncope include the following:

  • Environmental factors - Most commonly in a hot, crowded setting.
  • Emotional factors - Stress or the sight or threat of injury.
  • Physical factors - Standing too long with locked knees.
  • Illness - fatigue, hypoglycemia (low blood sugar), dehydration, or other current illness.


Situational syncope:


Susceptible people have episodes of syncope only in particular situations. Causes of situational syncope include the following:

  • Cough syncope occurs in people with lung disease when coughing forcefully.
  • Swallow syncope occurs upon swallowing in some people with disease in thethroat or esophagus.
  • Micturition syncope occurs when a susceptible person empties an overfilledbladder. It is most common in males who are intoxicated with alcohol.
  • Carotid sinus hypersensitivity occurs in some elderly people when turning theneck, shaving, or wearing a tight collar.
  • Postprandial fainting can occur in elderly people when their blood pressurefalls about an hour after eating.


Postural syncope: This occurs when a person lying down, who feels perfectly well and alert, sudden faints upon standing up. The brain's blood flow decreases when they stand owing to a drop in blood pressure. This sometimes occurs in people who have recently started or changed certain cardiovascular medications.


This type of fainting results from either or both of the following causes:

  • Low circulating blood volume, caused by blood loss (external or internal), dehydration, or heat exhaustion.
  • Impaired circulatory reflexes, caused by many medications, disorders of the nervous system, or congenital problems.


Cardiac syncope: Heart disease causes a person to faint by a variety of mechanisms. Cardiac causes of fainting are generally life threatening.


They include the following:

  • Cardiac rhythm abnormality (arrhythmia): Electrical problems of the heart impair its pumping ability. This causes a decrease in blood flow. The heart rate may be either too fast or too slow to pump blood well. This condition usually causes fainting without any warning symptoms.
  • Cardiac obstruction: Blood flow can be obstructed within the blood vessels in the chest. Cardiac obstruction can cause fainting during physical exertion. A variety of diseases cause obstruction, including heart attacks, diseased heart valves, pulmonary embolism, cardiomyopathy, pulmonary hypertension, cardiac tamponade, and aortic dissection.
  • Heart failure: The heart's pumping ability is impaired. This lowers the force with which blood circulates through the body and may decrease blood flow in thebrain.


Neurologic syncope: Neurologic problems cause fainting (or loss of consciousness) by various mechanisms.

  • Seizures are a cause of unconsciousness but are different from fainting. With seizures, the blood flow to the brain does not decrease. Unconsciousness results from disordered electrical discharges within the brain. Seizure typically causes prolonged (longer than 8 seconds) shaking of the arms and legs followed by confusion and disorientation after awakening.
  • Stroke (bleeding in the brain) can cause syncope associated with headache.
  • Transient ischemic attack (TIA or mini-stroke) can cause fainting, usually preceded by double vision, loss of balance, slurred speech, or vertigo (a spinning sensation).
  • Other rare causes include certain tongue problems and migraines.


Psychogenic syncope: Hyperventilation from an anxiety disorder can cause fainting. Rarely, people pretend to faint to minimize stress or for some recognized gain.


First Aid


If possible, help the person who has fainted to the ground to minimize injury.


Stimulate the person vigorously (yelling, briskly tapping). Call 911 immediately if the person does not respond.

Check for the pulse in the neck and begin CPR, if needed.


After the person recovers, encourage him or her to lie down until medical help arrives. Even if you believe the cause of the fainting is harmless, have the person lie down for 15-20 minutes before attempting to get up again.


Ask about any persistent symptoms, such as headache, back pain, chest pain, shortness of breath, abdominal pain, weakness, or loss of function, because these may indicate a life-threatening cause of the fainting.


The treatment of fainting depends on thediagnosis


Vasovagal syncope


  • Lifestyle alterations: Drink plenty of water, increase salt intake (under medical supervision), and avoid prolonged standing.
  • Medications: Medication may be prescribed if episodes are frequent.


Postural syncope


  • Lifestyle alterations: Sit up and flex calfmuscles for a few minutes before getting out of bed. Avoid dehydration. Elderly people with low blood pressure after eating should avoid large meals or plan to lie down for a few hours after eating.
  • Medications: In most cases, medications that cause fainting are withdrawn or changed.


Cardiac syncope


  • Medication and lifestyle alterations: These treatments are designed to optimize the heart's performance while limiting its demands. Controlling high blood pressure, for example, would call for a medication and lifestyle change. In some cases, specific anti-arrhythmic medication may be prescribed.
  • Surgery: Bypass surgery or angioplasty is used to treat coronary heart disease. For some valve problems, valves can be replaced. Catheter ablation is available to treat some arrhythmias.
  • Pacemaker: A pacemaker may be implanted to slow the heart in certain types of fast arrhythmias.
  • Implanted defibrillators are used to control life-threatening fast arrhythmias.
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