Seven years ago, Carol Weihrer, a flutist and office administrator, had her right eye removed. Ms. Weihrer had been living in pain from a severely scratched cornea for years and had already undergone 17 surgeries to try to fix it.

Just before she was given general anesthesia, she remembers feeling relieved that her trauma would soon be over. Suddenly, she woke up hearing disco music and thinking, “I must be done.” The next thing she said she heard was someone saying, “‘Cut deeper. Pull harder.’ I realized: They are not done. They are just starting.” She felt no pain, but was absolutely terrified.

“I can remember praying to God, screaming, but no sound came out,” said Ms. Weihrer, now 53, whose vocal muscles had been paralyzed by the anesthesia.

Such “anesthesia awareness” is not as rare as one might think. An estimated one to two out of every 1,000 patients – or 20,000 to 40,000 Americans a year – wake up under general anesthesia, according to a large study by Emory University researchers published last year.

(Patients given local or regional pain blocks plus “conscious sedation” are not unconscious to begin with and therefore cannot have anesthesia awareness.) General anesthesia is a combination of several drugs to block pain, paralyze the muscles so surgeons can cut tissue more easily, and to render patients unconscious and unable to remember the operation.

The Joint Commission on Accreditation of Healthcare Organizations, which accredits 85% of American hospitals, recently described the condition as “under-recognized” and “under-treated” and said hospitals and doctors should develop policies for avoiding it.

To this day, Ms. Weihrer, who now runs the Anesthesia Awareness Campaign, Inc. from her home in Reston, Va., can’t sleep lying down because it brings back too many vivid memories.

Like many patients who wake up during anesthesia, she is being treated for PTSD, post-traumatic stress disorder, which includes flashbacks, irritability, and exaggerated startle responses. She can’t sleep more than a few hours without nightmares, and still can recall verbatim doctors’ conversations in the operating room.

“Patients don’t want to talk about it because they have a hard time believing it could happen to them, and anesthesiologists don’t really want to acknowledge they have issues like that,” said Dr. Michael England, senior anesthesiologist at New England Medical Center.

Already, there have been roughly a dozen anesthesia-awareness lawsuits nationwide, according to a recent issue of Law.com, an online legal newsletter.

Ms. Weihrer sued her anesthesiologist for malpractice, arguing, among other things, that an anesthesia machine was not working properly. The case was settled.

Some patients, like John Robinson, a psychologist in Carmichael, Calif., block out the experience for years, until some trigger brings it to mind.

Mr. Robinson, now 58, had open-heart surgery at 14 to correct a faulty heart valve.

“I woke up in surgery and experienced hands working inside my heart and my body being very cold, numb, paralyzed with my chest torn open. All of this was profoundly frightening,” he said. But Mr. Robinson repressed the entire episode – until 40 years later, when he had an abnormal heart rhythm and went to the emergency room, where doctors shocked his heart back to a normal rhythm.

“That awakened all these body memories of the surgery,” he said. “I began to walk around feeling literally as if my chest were open. I got in touch with this immense anguish – this abandoned 14-year-old, and nobody knowing about it.” He said he had to give up his counseling practice because he “lost the ability to go knee-deep into the horrors and traumas of other people.”

The fact of being awake while surgeons operate can lead to post-traumatic stress disorder, said Dr. Janet Osterman, vice-chairwoman of psychiatry at Boston University School of Medicine and lead author of a 2001 paper on the subject.

But cognitive-behavioral therapy and eye-movement desensitization and reprocessing therapy, both of which involve getting patients to imagine the trauma and learn to dampen their emotional arousal to it, can help overcome the trauma, Dr. Osterman said.

To be sure, some cases of anesthesia awareness are tough to avoid. If a patient already has low blood pressure, anesthesiologists deliberately keep the patient only lightly asleep so as not to depress blood pressure further.

But often, anesthesia awareness is a genuine mistake that, until the last few years, doctors had no good way to detect – though increases in heart rate and blood pressure, or leaking of tears from the eyes, are clues.

Now, some anesthesiologists and nurse anesthetists use brain-wave monitors such as the Bispectral Index system developed by Aspect Medical Systems in Newton, Mass., to gauge the patient’s level of consciousness.

Other companies, including Physiometrix in Billerica, Mass., also make brain-activity monitors.

Two studies published this year, one in Sweden and one in Australia, showed these monitors can reduce the incidence of awareness episodes.

So far, though, the American Society of Anesthesiologists and the American Association of Nurse Anesthetists believe it’s too soon to recommend that the monitors be used routinely.

In the meantime, if you are facing surgery or think you have had an anesthesia awareness experience, there are things you can do. Before surgery, Ms. Weihrer suggests asking your doctors to use a brain activity monitor.

Also, be sure to tell your anesthesiologist if you have had an episode of awareness in the past, said Dr. John Ulatowski, anesthesiologist in chief at Johns Hopkins Hospital. If you do wake up under anesthesia and can remember the episode, tell your doctors.

If immediate psychiatric help is not offered, ask for it.

Ms. Foreman is a lecturer on medicine at Harvard Medical School. Her columns are available at www.myhealthsense.com