Nightmares have fascinated and perplexed people for centuries, their meaning debated by therapists and analysts of all schools of thought, their effects so powerful that one terrifying nightmare can affect a person for a lifetime.

A nightmare is “a disturbing dream experience which rubs, bites and sickens our soul, and has an undercurrent of horsepower, lewd demons, aggressive orality and death,” Dr. White-Lewis wrote in “In Defense of Nightmares,” her contribution to a 1993 book of essays about dreams.

From 4 to 8 percent of adults report experiencing nightmares, perhaps as often as once per week or more, according to sleep researchers. But the rate is as high as 90 percent among groups like combat veterans and rape victims, Dr. Krakow said. He said treatment for post-traumatic stress needed to deal much more actively with nightmares.

He and other clinicians are increasingly using imagery rehearsal therapy, or I.R.T., to treat veterans and active-duty troops in the Iraq and Afghanistan wars. Last month, Dr. Krakow conducted a workshop on imagery rehearsal and other sleep treatments for 65 therapists, sleep doctors and psychiatrists, including many working with the military. And the technique has drawn more attention from other researchers in the last several years. Anne Germain, an associate professor of psychiatry at the University of Pittsburgh School of Medicine, is comparing two treatments  behavioral therapy, including imagery rehearsal, and the blood-pressure drug prazosin, which has been found to reduce nightmares.

Preliminary results from a study of 50 veterans showed that both treatments were effective in reducing nightmares and symptoms of P.T.S.D., she said, though they differed from patient to patient. She is continuing to study what factors may lead to those differences.

Deirdre Barrett, a psychologist at Harvard Medical School who is an expert on dream incubation, inducing dreams to resolve conflicts , and on the connection between trauma and dreams  said she was struck by the growing interest in nightmares as a result of war trauma and torture.