Feel like you're falling apart, going to pieces? Arms and legs feel like jelly? Bothered by headaches, neck and back pains?

These may be symptoms of anxiety, a fairly common and treatable psychiatric disorder that in most extreme forms can be disabling, says a Duke University Medical Center psychiatrist.

Perhaps as many as 20 million Americans may suffer unknowingly from anxiety, says William W.K. Zung, Duke professor of psychiatry. Zung said a recent study found 20 percent of 739 consecutive patients seen in a family medicine clinic had significant symptoms of anxiety.

"The nine-month study was surprising because it suggested that anxiety may be more prevalent in the general population than previously believed, more common even than depression," he says. "It's something that family practitioners should be on the lookout for."

The study also found that symptoms of anxiety tended to increase with age and seemed to affect more women than men.

Duke University, in Durham, N.C., recently started an Anxiety Disorders Program.

Anxiety, he says, can disrupt sleep, upset the stomach; symptoms may include shakes and aches, dizziness and sweating.

A fear of flying or other phobias, panic attacks and post-traumatic stress disorder are some of the forms anxiety takes, says Zung.

"Generalized anxiety disorder involves fundamental biologic changes that result from a patient's attempt to cope with and adapt to stress," Zung says, stress that may be internal, external, or both.

Anxiety can be treated with medication, he says, as well as psychotherapy, behavioral therapy and biofeedback.