Brain & Nervous System Health Center

Understanding Fainting -- the Basics

What Is Fainting?

Fainting, also called syncope (pronounced SIN-ko-pee), is a sudden, brief loss of consciousness and posture caused by decreased blood flow to the brain.

Many different conditions can cause fainting. These include heart problems such as irregular heart beats, seizures, low blood sugar (hypoglycemia), anemia (a deficiency in healthy oxygen carrying cells), and problems with how the nervous system (the body's system of nerves) regulates blood pressure. Some types of fainting seem to run in families.

While fainting may indicate a particular medical condition, sometimes it may occur in an otherwise healthy individual. Fainting is a particular problem for the elderly who may suffer serious injuries from falls when they faint. Most episodes are very brief. In most cases, the individual who has fainted regains complete consciousness within just a few minutes.

Fainting is a common problem, accounting for 3% of emergency room visits and 6% of hospital admissions. It can happen in otherwise healthy people. A person may feel faint and lightheaded (presyncope) or lose consciousness (syncope).

What Causes Fainting?

Fainting may have a variety of causes. A simple episode, also called a vasovagal attack or neurally-mediated syncope, is the most common type of fainting spell. It is most common in children and young adults. A vasovagal attack happens because blood pressure drops, reducing circulation to the brain and causing loss of consciousness. Typically an attack occurs while standing and is frequently preceded by a sensation of warmth, nausea, lightheadedness and visual "grayout." If the syncope is prolonged, it can trigger a seizure.

You may suffer from a simple fainting spell due to anxiety, fear, pain, intense emotional stress, hunger, or use of alcohol or drugs. Most people who suffer from simple fainting have no underlying heart or neurological (nerve or brain) problem.

Some people have a problem with the way their body regulates their blood pressure, particularly when they move too quickly from a lying or sitting position to a standing position. This condition is called postural hypotension and may be severe enough to cause fainting. This type of fainting is more common in the elderly, people who recently had a lengthy illness that kept them in bed and people who have poor muscle tone.

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The following can cause fainting, too:

  • Diseases of the autonomic nervous system. Your autonomic nervous system is the part of the nervous system that controls involuntary vital functions, such as the beating of your heart, the degree to which your blood vessels are constricted, and breathing. Autonomic nervous system problems include acute or subacute dysautonomia, chronic post-ganglionic autonomic insufficiency, and chronic pre-ganglionic autonomic insufficiency. If you have one of these disorders, you are likely to have other symptoms, such as erectile dysfunction (inability to have or maintain an erection), loss of bladder and bowel control, loss of the normal reflexes of your pupils, or decreased sweating, tearing, and salivation.
  • Conditions that interfere with the parts of the nervous system that regulate blood pressure and heart rate. These conditions include diabetes, alcoholism, malnutrition, and amyloidosis (in which waxy protein builds up in the tissues and organs). If you take certain high blood pressure drugs, which act on your blood vessels, you may be more likely to suffer from fainting. If you are dehydrated, which may affect the amount of blood in your body and, thus, your blood pressure, you may be more likely to faint.
  • Heart or blood vessel problems that interfere with blood flow to the brain. These may include heart block (a problem with the electrical impulses that control your heart muscle), problems with the sinus node (a specialized area of your heart that helps it beat), heart arrhythmia (irregular heart rhythm), a blood clot in the lungs, an abnormally narrowed aortic heart valve, or certain other problems with the structure of your heart.
  • Conditions that may cause unusual patterns of stimulation to particular nerves. These include micturition syncope (fainting during or after urination), glossopharyngeal neuralgia (fainting due to inflammation and pain in a particular nerve to the mouth); cough syncope (fainting after intense coughing), and stretch syncope (fainting that occurs when stretching the neck and arms).
  • Hyperventilation. If you become intensely anxious or panicked and breathe too quickly, you may feel faint from hyperventilation (taking in too much oxygen and getting rid of too much carbon dioxide too quickly).

 

WebMD Medical Reference Reviewed by Jennifer Robinson, MD on March 04, 2015

Sources

SOURCES: 

Heart Rhythm Society. 

American Academy of Family Physicians. 

The Merck Manual.

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