Your heart suddenly starts pounding so hard you think it's going to leap right out of your chest. You're sweating even though it's cold out. You feel unsteady on your feet and generally shaky, like the world around you is spinning out of control and you can't get a grip. Your hands and feet are numb and useless. You're gasping for breath and feel like you're drowning.

If you have felt all of these come on without warning, you may have just suffered a panic attack. This frightening constellation of symptoms affects women twice as often as men, although scientists are not sure why. Genetics may be part of the explanation; women are more prone to anxiety or depression, and a history of these mood disorders makes you more likely to have a panic attack. But life experiences such as childhood sexual abuse (more common in girls than boys) may also increase women's vulnerability.

A particularly active area of research at the moment is the effect of hormones. Women seem most susceptible to panic attacks during times of hormonal changes, such as adolescence, pregnancy and menopause. Dr. Lilian Gonsalves, vice chair of the department of psychiatry and psychology at the Cleveland Clinic, says some scientists think that hormonal fluctuation may upset the balance of chemicals in the brain that modulate fear and anxiety, triggering a panic attack.

Many women report experiencing their first panic attack in late adolescence. But others have no trouble until they reach perimenopause, the years before they stop menstruating, when their hormone levels often vary wildly. "These are high-functioning women who have never seen a psychiatrist before," says Gonsalves. "As their periods change, they start having hot flashes and they don't sleep. They become acutely anxious."

"Acute" is the key word here, and it's what distinguishes a panic attack from general anxiety. A panic attack feels like the fight-or-flight response gone wild with no provocation. You can be standing at a bus stop or shopping at the mall without any danger in sight, and suddenly, you feel like you're dying. The attack is generally over in a few minutes, but sometimes symptoms—especially feeling faint and dizzy—can linger for more than an hour. It's estimated that about a quarter of people who visit the ER complaining of chest pain are actually suffering from a panic attack. Most panic attacks take place in the daytime, but it's possible to have one even while you're sleeping. In nocturnal panic attacks, you wake up with all the same symptoms.

Fear of another attack often makes people avoid places where an attack took place, and a small percentage of sufferers may eventually become housebound, a condition called agoraphobia. Suffering from frequent panic attacks also means you are at higher risk of depression, substance abuse and suicide. Some research also indicates that women who have repeated attacks are at higher risk of death. "We used to say that you don't die of a panic attack, but I've stopped saying that," says Gonsalves. "It could be that during a panic attack you get coronary spasms or an irregular heart rate."