For the hypochondriac, every little twinge forecasts imminent demise. That dull ache just behind the eyes -- could it be a brain tumor? Those funny tingles -- multiple sclerosis? A sudden shortness of breath -- doubtless a heart attack in the making. The hypochondriac scans his body like a prison guard: Every organ, every cell is on the verge of flaring up into full-scale rebellion.

Not only are hypochondriacs' bodies working against them; so, sometimes, are unsympathetic doctors, who label them "crocks," "trolls," "turkeys," "nomads," "doctor-shoppers," "problem patients," "neurotics," "malingerers" and "GOMERs" (for Get Out of My Emergency Room). At the same time, their families tolerate and often unconsciously welcome them -- something that ultimately does not help.

During any one week, an estimated 60 to 80 percent of healthy individuals experience bodily complaints (ringing in ears, abdominal spasms, back pain, itching) in the absence of a physical disease. And some will seize on these symptoms: An estimated 10 to 20 percent of the population has periodic and irrational worries about illness. These could range from bone cancer after watching a television special to AIDS after scanning almost any newspaper. For a minority, these fears become a habit.

"The absolute minimum of intermittent worriers would be 10 percent, and it may well be higher," says Charles V. Ford, professor of psychiatry at the University of Arkansas for Medical Sciences and a specialist on hypochondria. Does the medical community agree with this figure?

"If you're asking whether a large percentage of doctors think it is accurate, yes," he says. "But it doesn't seem to change their approach to their patients. They continue to react as though every patient who comes in has legitimate physical symptoms."

Ford adds that there's a second group who have a little bit of organic dysfunction but, if they didn't also have psychological problems, wouldn't be seeking medical care. Take, for example, colds and upper respiratory infections. Most sufferers with these ailments don't seek out a doctor. What factors, then, influence someone to do so?

"These people are going because they are concurrently under some kind of stress," he explains. "They are what is described as 'amplifiers,' because they tend to overreact to and overinterpret their physical symptoms. For each one in the doctor's office, there are another three with the same degree of sickness who are not seeking medical care."

Susan Baur, author of Hypochondria: Woeful Imaginations (to be published next month by the University of California Press), defines hypochondria as "a fear of disease so great it disrupts normal living. There can be real physical problems, but the fear or preoccupation is way out of proportion to anything that's really there."

Although the condition is not going to strike everyone on the planet, she says, "I don't think there are many people who don't have some ability to empathize with that sudden 'Oh my God, I'm gonna die!' In some cases, this is a justifiable reaction to a real threat, such as a heart attack. But in many other instances, it's a momentary overreaction to what is in fact a minor headache, stomachache or other physical symptom received under stress."

Although the definition of hypochondria sounds relatively simple, Baur points out that "one of the most difficult paths confronting doctors is to distinguish among hypochondriacs, invalids, chronic complainers, malingerers, the overanxious, the worried well -- and the physically ill. It's not a simple diagnosis."

The Whiteley Index is one of the questionnaires used to identify types of hypochondriacs. Some of the questions (Do you often worry about the possibility that you have a serious illness?) are answered affirmatively by those sufferers willing to acknowledge their terrors. Other queries indicate greater-than-usual bodily preoccupations (Are you bothered by many aches and pains?) or a phobia about illness (If a disease is brought to your attention through radio, TV, newspapers or someone you know, do you worry about getting it yourself?)

Masterpiece Theatre host Alistair Cooke used another method of analysis in his speech "Hypochondria: The Layman's Specialty." His hypochondriacs include the folkloric (believes everything he has been told, and consequently "fights a winning battle against his intelligence"); the fatalistic (takes "an instinctively dramatic view of life and therefore believes in instant cures and instant damnation"); the smart aleck ("there is a new drug, and in acquiring it he conveys that medicine has been floundering in a dark tunnel since Hippocrates and has at last seen the light"); the martyr ("apparently devoted throughout a long marriage but is never free from several chronic ailments"); and the happy (The difference between the happy and the unhappy "is no more, but no less, than the difference between an unsuccessful and a successful show-off.") Cooke placed himself (spastic colon, diverticulosis, inflamed duodenum, muscle spasms, flat feet, tendency to argue with himself while alone, etc.) into this last group.

Sounds likely enough, but doctors don't agree on what causes a person to become hypochondriacal. Explanations range all the way from inability to separate from their mothers to physiological factors. Meanwhile, new research seems to indicate what many hypochondriacs have long suspected: They simply have super-sensitive bodies.

"To use a simple example: If I came up behind you and clapped my hands loud in your ear, you'd probably jump," Baur says. "If I did it a second time, you'd jump less. A third time, you wouldn't jump at all. You'd become habituated. Hypochondriacs are those who, when you clap in their ears, jump all six times."

Baur, 48, understands this from immediate experience. "I had a traumatic operation as a young child and was left with a real fear of hospital smells and shots. So I know the brand of terror," she says. The author of an award-winning book on oceanography, she's switched careers and is now a psychology intern in a Massachusetts V.A. hospital.

As material for study, she says, hypochondria is particularly attractive because it's such a human dilemma. "It's not nearly as straightforward as someone having their legs cut off, or even suffering from cancer. There the fight is clearly drawn: the body against the disease. If you win, you live longer. With hypochondria, you're fighting yourself. It's more fascinating to a writer, and more tortuous to a victim, than any other illness."

Hypochondria is a millenniums-old affliction that is now receiving an increased amount of attention. On the one hand, soaring health costs could be partially alleviated by using short-term psychotherapy to address the underlying problems of hypochondriacs. Yet, even if doctors and psychiatrists could begin to get the worried well out of waiting rooms, a disease has come along that may do the reverse. "AIDS is a perfect disease for hypochondriacs," says Baur. "The symptoms are diffuse and unpredictable, and shame and guilt is an intrinsic part. It may end up standing in the same place as syphilis, which was one of the greatest fears of hypochondriacs in the 18th and 19th centuries."

She gets on my nerves. He's a pain in the rear. I can't shoulder this load. You make me want to puke.

Phrases like these are uttered unthinkingly, but sometimes there can be more truth than the speaker realizes. Emotional experiences -- from trouble with your boss to a spat with your spouse -- can commonly cause physical symptoms.

Some individuals have been particularly sensitized to emotional pain because of circumstances in their formative years. As a result, they develop physical symptoms as a way of warding off that emotional anguish. It's more socially acceptable to be sick and have to be cared for than to be depressed and want the same thing.

"These people are saying with their symptoms what they don't recognize and can't verbalize," says George Becker, the director of consultation psychiatry at Pacific Presbyterian Medical Center in San Francisco. "It's a process of conversion, in which emotional pain is transformed into pain that seems to be physical in origin, but which is not. Trying to heal these patients involves slowly making unconscious things conscious, so they recognize what their true feelings are."

Becker is an unusual physician. He was an orthopedic surgeon when he began to realize that between a quarter and a third of his patients did not have an obvious physical ailment. Intrigued, he went back to school a decade ago and became a psychiatrist; now, he uses both specialties to treat chronic pain. "I don't like the term 'holistic health' because of the flower-child overtones," he says, "but I do feel the whole person must be attended to -- from a musculo-skeletal standpoint and a psychological one."

In Latin, the word "pain" has a common root with "suffering" and "atonement." Hypochondriacal pain -- which is very real; back pain that derives from emotional conflict hurts just as much as back pain from a ruptured disc -- may represent an attempt on the part of the patient to atone for guilt that exists outside of conscious awareness. "What better way," Becker asks, "to punish oneself than to be wounded by the surgeon's knife?"

The guilt often comes from early experiences, where it is associated with physical or emotional abandonment -- a parent who dies or leaves; parental alcoholism; losing a sibling.

"A normal child wants to get rid of a brother or sister out of sibling rivalry," says Becker. "If there then is a death, the survivor may be haunted by unconscious guilt. He unconsciously reasons, 'I wanted my sibling dead; now he is dead; it must be my fault, because I thought about it.' Or if a parent leaves by divorce, the thought pattern is: 'I must be worthless, because otherwise they would have stayed together.' And with children who are battered or sexually molested: 'I am worthless, and that's why I'm maltreated.' "

But it's not only childhood experiences that precipitate hypochondriacal symptoms. Becker mentions another patient, a woman in her seventies whose husband was dying of cancer. She arrived at the cardiac care unit with what seemed to be a heart attack -- crushing chest pain that radiated down her left arm.

All the medical tests showed nothing wrong, however, so Becker tried a combination of psychotherapy and an anti-depressant medication -- a treatment that was soon effective. "Her problem was anger at the burden imposed by the illness and depression at the loss of a loved one," he says. "These are normal emotions. Her symptoms reflected her heartbreak."

There's an old joke about the hypochondriac's tombstone, which reads: "I told you I was sick." Part of the difficulty physicians have with this disorder is the fear of missing a diagnosis -- of unwittingly telling a cancer victim his problem is emotional.

"If someone comes to you with a physical complaint, you work them up and don't find any organic illness, that doesn't in and of itself mean the patient is hypochondriacal," warns Becker. "A positive diagnosis of hypochondria can be made only after rather strict criteria."

While the deaths continue to rise among drug users and homosexuals, the latest word on AIDS for heterosexuals has been: remain vigilant, but relax. The secretary of Health and Human Services has reversed his earlier forecast of a wildfire epidemic. The heterosexual breakout does not seem to be happening.

In less than two weeks, however, sharply different news will be delivered by the team of Masters and Johnson, with the assistance of Dr. Robert C. Kolodny. Crisis: Heterosexual Behavior in the Age of Aids asserts, according to the publisher's publicity, "that huge numbers of infections with the AIDS virus are smoldering in the heterosexual population, and that it is just a matter of time before this fact explodes into public awareness."

Hype or truth? Kolodny said that "I can't speak with any reporter on anything having to do with the topics of AIDS or our book. We are absolutely prohibited until the day of the press conference on March 7 from saying anything."

In any case, a debate over Crisis could reactivate those newly dulled fears among heterosexuals. Where, in worrying about AIDS, does the rational become irrational, the smart approach turn into hypochondria? Should a sexual encounter six years ago in Manhattan produce the same anxiety level as one six months ago in Manhattan, Kan.? Do safe sex and serial monogamy (no more than one sexual relationship at a time) place an acceptable limit on the threat to your health?

Ford, the University of Arkansas specialist, gives this answer: "When you get on an airplane, you worry a little about it crashing. And I suspect a little bit of worry is healthy, normal and reality-testing. But if you're afraid to get on the plane, that's irrational.

"All of us have to worry about AIDS. But even for people who have engaged in some behaviors that might have increased their risk, the worry is inappropriate if it comes to dominate their life and prevents them from pursuing their usual activities. To refuse dental care for fear of contracting AIDS would be unreasonable. Most people, however, would regard caution about sexual partners as entirely prudent."

He doesn't, however, feel there will necessarily be an increase in the number of hypochondriacs. "Before AIDS, they had herpes, reactive hypoglycemia, environmental toxins -- any number of fad diseases. They'll just pick this up as their new concern."

A certain degree of preoccupation with health and illness could be a good thing, even if some people would label it hypochondriacal. In the mildest cases, it merely expresses itself as careful behavior.

"I view it as being overly cautious," says one 37-year-old Washington woman who works in the arts. "It's not macho, not brave. I succumb to fear for my heath."

At this moment, she says, "I have a pain in my ankle. Every night when it throbs, I think: 'Either I've got to get a new pair of running shoes, or I've got phlebitis.'

"Frankly," she adds, "I think hypochondriacs are a little more intelligent. They think about things, analyze them. They know a body is fragile. You have to be smart and take care of it. I've lost a parent, and know life isn't forever."

Exultant feelings of well-being aren't forever either. Robert Kellner, vice chairman of psychiatry at the University of New Mexico and a specialist on hypochondria, wishes more sufferers would realize that bodies are hardly ever as sparky or peppy as television commercials would have you believe.

"If one of us has a week without getting a headache, stomachache, joint pains, that was a lucky week," he says. "People should not hope to feel absolutely well and energetic all the time. Our bodies last for about 75-odd years, but they are not perfect. They're good enough to ski down slopes and lift heavy weights, but not free from squeaks and odd cramps."

A survey Kellner did in both New Mexico and England -- and which, he says, has since been corroborated by other studies -- indicated that more than 40 percent of people feel tired in any one week without an obvious physical cause -- "like having played tennis for six hours or staying up til 4 a.m. the night before," the doctor says.

"Makes you feel normal, doesn't it?"