A man in his mid-40s is rushed to an emergency room. He is sweating, his heart is racing, and he can't catch his breath. He and his wife are convinced he is having a heart attack. He could be-only, this time, the ER doctors tell him his heart is just fine. What he's having is a panic attack.

Though no one should ever ignore heart attack symptoms or assume one is having a panic attack instead, thousands of people each year share this man's experience.

Panic attacks are truly terrifying and can happen without warning or reason, causing sudden fear and extreme nervousness for 10 minutes or more. Physical symptoms intensify the attack: sweating, racing heart, rapid pulse, feeling faint or as if one is choking, and-perhaps worst of all-the sense of "going crazy."

These attacks are a symptom of panic disorder, a type of anxiety disorder that affects some 2.4 million U.S. adults. The disorder most often begins during the late teens and early adulthood and strikes twice as many American women as men. No one knows what causes panic disorder, though researchers suspect a combination of biological and environmental factors, including family history (panic disorder seems to run in families), stressful life events, drug and alcohol abuse, and thinking patterns that exaggerate normal physical reactions.

What happens, exactly? "We all physically respond to stress," says Barbara O. Rothbaum, PhD, psychiatry professor and director, Trauma and Anxiety Recovery Program, at Atlanta's Emory University School of Medicine. "You might feel anxious about work-related problems, taking a big exam, or making an important decision. But someone who suffers from panic disorder may react to those same moderate pressures with an exaggerated physical reaction-as if he or she were about to be attacked by a wild tiger or fall from a great height. It's full-on, adrenaline-pumping, fight-or-flight response."

For this very reason, Rothbaum says, panic attacks are doubly frightening. "Because there is no real danger that provokes them, these episodes can happen anytime, anywhere"-including while walking down the street, dining out with a group of friends, grocery shopping-even sleeping, according to the National Institute of Mental Health.

Over time, many who suffer panic attacks develop an on-going fear of having another attack. This fear can severely hamper daily activities and overall quality of life. Some people refuse to leave their houses or to put themselves in situations that remind them of their previous attacks. Agoraphobia (a fear of being outside of known and safe surroundings) or other mental problems may follow.

Fortunately, panic disorder is one of the most treatable of the anxiety disorders. Psychotherapy (sometimes called talk therapy), cognitive, or biofeedback therapy can all help alter a person's response to stimuli. Medications, such as antidepressants and beta-blockers, are another option. And certain lifestyle changes, such as limiting caffeine and sticking to a daily exercise plan, can decrease symptoms as well.