You are in the grocery store when suddenly, for no apparent reason, you are gripped by terror. Your heart races, you can't catch your breath, your muscles tense up, your hands tingle, you break into a sweat and feel faint. The sensations are so unexpected and overpowering that you think you are going to die or lose your mind right there at the checkout counter. Within a couple of minutes, the episode passes almost as abruptly as it began. Although there are no residual physical effects, you worry about your health.

Over the next few weeks, your anxiety rises at the mere thought of having another panic attack. Your anxiety grows so intense it begins to disrupt your work and family life. Over the next few months, you begin avoiding social situations, figuring if another panic attack strikes, at least you'll suffer through it in the privacy of your own home.

If this scenario sounds familiar, you may be among the more than 19 million Americans with one or more anxiety disorders, an umbrella psychiatric diagnosis that includes panic disorder, generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and phobias. As with many other mental illnesses, anxiety disorders are chronic, unremitting, and may grow worse unless properly treated. Sufferers may be tormented by episodes of panic, irrational thoughts and fears, compulsive behaviors or rituals, flashbacks, nightmares, or numerous frightening physical symptoms. Other problems, such as substance abuse or depression, often accompany anxiety disorders.

While there is no cure for any of the anxiety disorders, there are many effective treatments to relieve symptoms and greatly improve your quality of life. Unfortunately, a large percentage of sufferers never gets properly diagnosed or treated, mainly because of the social stigma attached to anxiety disorders and other mental health problems.

What causes anxiety disorders?

No one has pinpointed the precise cause of anxiety disorders, but there are many theories as to their origin. As with other psychiatric illnesses, anxiety disorders are probably rooted in biology, psychology, social circumstances, and environment to varying degrees. Panic disorder, for example, may stem partly from an overproduction of the "fight-or-flight" hormones epinephrine and norepinephrine deep within the brain stem. An imbalance of the brain chemical, serotonin, which is believed to play a major role in mood regulation, also may be involved.

Some people inherit a tendency toward an anxiety disorder, which can run in families. A genetic predisposition may be triggered or exacerbated by distorted thinking and learned behaviors. For example, fear of future panic attacks (or even the fear of fear itself) may distort people's perception of normal physiological fluctuations. Mentally healthy people think nothing of sweat on a warm day, or noticing a subtle change in their heart rate when someone they are attracted to enters the room. But someone with an anxiety disorder may perceive those same physiological changes as harbingers of doom. Researchers have also found that certain environmental stresses, such as the death of a loved one, getting divorced, moving to a different city, or starting college, may precipitate or aggravate anxiety disorder symptoms.