Why do people faint?

Q. Why do people faint?

A. Fainting, also called syncope, is a sudden and brief loss of consciousness followed by a spontaneous return to wakefulness — people who “black out” and then “come to” on their own without outside intervention. During the faint, they’re in danger of falls and injuries if they lose muscle control.

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There are several possible causes of fainting, but they all stem from a temporary decrease in blood flow to the brain. The typical Victorian-era swoon is one of the most common forms, called vasovagal syncope. Lewis Lipsitz, a geriatrician at Beth Israel Deaconess Medical Center and Hebrew SeniorLife, explains that it’s caused by a reflexive response to a stimulus, such as stress, a sudden shock, or the sight of blood.

Fainting without an obvious trigger can be a sign of an underlying health problem, such as an irregular heart rhythm, heart disease, or severe dehydration.

“The elderly have syncope more commonly than any other group,” Lipsitz says, which can put them at risk of falls and fractures. Often the spells are caused by actions as simple as changing position or eating a meal. When we stand up, Lipsitz says, “about half a liter of blood immediately goes to the legs and the lower abdomen,” and eating also pulls blood from the brain to the gut. Our bodies compensate by raising the heart rate to get blood to the brain. But elderly people can’t always restore their blood flow, and dehydration or certain medications can exacerbate the problem.