If a person is feeling faint, unconsciousness may be prevented by sitting with the head between the knees, as shown in the illustration, or by lying flat with the legs raised.
Illustration by Electronic Illustrators Group. © 2016 Cengage Learning®.
Fainting is a brief loss of consciousness caused by a temporary drop in blood flow to the brain.
One minute, Marie Osmond was finishing a performance with her partner on the television show Dancing with the Stars and waiting for their scores from the judges. The next minute, she was peering up at the concerned faces of her dance partner and the show's host. She had just had a fainting spell, and this was not her first. The 2007 incident made the news because it happened on live TV to a famous person, but fainting is common. As often happens with people who experience fainting spells, Osmond recovered within minutes and had no lasting effects from the incident.
Fainting, also known as syncope (SING-ko-pee), is a brief loss of consciousness caused by a temporary drop in the flow of oxygen-carrying blood to the brain. Without enough oxygen, brain processes slow down, and the person may pass out briefly. The sudden drop in blood flow can occur for several reasons, including an irregular heart rate or rhythm, a dip in blood pressure, or the pooling of blood in the legs usually after a prolonged period of standing. Although fainting can be frightening and embarrassing, it usually is not a cause for panic. Healthy people sometimes faint when they are extremely tired, get bad news, or see something upsetting. In other cases, however, fainting may be a sign of a more serious medical condition.
The most serious causes of fainting usually involve the heart or blood vessels. In some cases, the heart beats too fast or with an irregular rhythm, reducing the amount of blood it pumps. In other cases, individuals may have a narrowing of the valve that lets blood out of the heart or a partial blockage of the blood vessels that carry blood to the head, limiting blood flow to the brain.
Stress, fright, or sudden pain can arouse the nervous system, which, in turn, can signal the heart to slow down or the blood vessels to widen. If such changes happen too quickly, a person's blood pressure can drop suddenly, which reduces blood flow to the brain, and the person may faint.
Sweat contains sodium, a mineral that plays a key role in blood pressure control. Heavy sweating is another possible cause of a sudden dip in blood pressure. People who take part in strenuous physical activities under hot, humid conditions may experience this problem.
When most people stand up, the nervous system * triggers a reflex response that increases the heart rate and blood pressure. This response ensures that enough blood gets to the brain. In some people, particularly the elderly, these responses may not occur quickly enough. Blood may pool in the legs. When too little blood reaches the brain, the person may faint.
Some people simply lose consciousness and slump down without warning. However, many people feel dizzy, lightheaded, or sick to their stomach just before they faint. They may become sweaty and pale, and they may have a graying out of vision. By definition, a faint does not last long. Falling down locates the head at the same level as the heart. This position helps restore blood flow to the brain. The person soon regains consciousness, usually within a minute or so.
A person who is feeling faint should lie down immediately and not try to stand or walk. If the person who faints does not regain consciousness within a minute or two, someone must get emergency medical help for that person. While awaiting emergency help, adult bystanders should elevate the legs of the person who has fainted; loosen belts, collars, or tight clothing; and check that the person's airway remains open, because people who faint may vomit as well. They should not move the person who has fainted until medical help arrives, because the fall may have injured the person.
The person who has fainted probably will regain consciousness quickly but may continue to feel a bit weak for a little while. To prevent fainting again, the person should continue lying down for a few minutes.
Even when people recover promptly, they should contact their doctors about a first fainting attack, about repeated fainting spells, or about other possible symptoms, including irregular heartbeat, chest pain, shortness of breath, blurred vision, confusion, or trouble talking.
See also Heart Disease: Overview • Hypertension • Stress and Stress-Related Illness
Pavri, Behzad. B, and Andrew E. Epstein, eds. Handbook of Syncope: A Concise Clinical Approach. New Delhi: Jaypee Brothers Medical Publishers, 2014.
MedlinePlus. “Fainting.” U.S. National Library of Medicine, National Institutes of Health. https://www.nlm.nih.gov/medlineplus/ency/article/003092.htm (accessed December 5, 2015).
New Jersey Center for Fainting. “All About Fainting.” http://www.njfaint.com/education/fainting/fainting3.html (accessed December 5, 2015).
American Heart Association. 7272 Greenville Ave., Dallas, TX, 752314596. Toll-free: 800-AHA-USA1. Website: http://www.heart.org (accessed December 5, 2015).
Heart Rhythm Society. 1325 G St. NW, Suite 400, Washington, DC 20005. Telephone: 202-464-3400. Website: http://www.hrsonline.org (accessed December 5, 2015).
* nervous system is a network of specialized tissue made of nerve cells, or neurons, that processes messages to and from different parts of the human body.