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Brain & Nervous System Health Center

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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.

Understanding Fainting

Find out more about fainting:



Diagnosis and Treatment


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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