I was about halfway through Catherine Belling’s new book, “A Condition of Doubt: The Meanings of Hypochondria,” when I realized that I had been annotating with a pen that had the words “Absolute Death” written on its side.

Absolute Death happens to be the Brooklyn extermination service that my wife and I use. But to someone ceaselessly concerned with his health and in the midst of reading about disease, this was a sign from the gods—and not a good one. Hostile forces had recently been gathering at my corporeal borders: moles, lumps, pains. The pen coalesced these into a single, dreadful assault on my well-being. “Our name says it all,” read the tagline on the ominous writing utensil. This was truth in advertising taken to a perverse degree.

Such thinking—restless in the weaving of connections, apocalyptic in its conclusions—is the hypochondriac’s daily routine. It takes no small amount of ingenuity to extrapolate from Have I forgotten my iPhone again? to I must have Alzheimer’s, but we are always ready for disaster, if never quite ready enough. In one clever passage, Belling, a medical historian at Northwestern, compares the condition to a poster for Steven Spielberg’s “Jaws” that shows a woman swimming on the surface of a seemingly bottomless ocean, while a shark rises up towards her from the deep. She is at once unsuspecting and on the point of death. A crucial distinction: what we fear is not the shark itself, but the naïveté with which its prey calmly treads the water.

Hypochondria is an obsession with what lurks below. The word comes from “hypochondrion,” a term that Hippocrates used to refer to the area under the chondros, or the diaphragm. Later, during the Christian era, when leeches were the vanguard of medicine, it was thought that an excess of black bile caused the ailment. In “The Anatomy of Melancholy,” a famous 1621 chronicle of ills bodily and mental, Robert Burton refers to “hypochondriacal melancholy” as “a disease so grievous, so common, I know not wherein to do a more general service…than to prescribe means how to prevent and cure so universal a malady.”

Whatever service Burton hoped to provide with his book appears to have fallen short. As the Scientific Revolution codified medical knowledge and made it more accessible, it empowered the masses to be more intelligently afraid. It had been easier to suppose that demons were responsible for your illness. Those, at least, you could try to pray away. But what are you to do with errant cells and blocked arteries?

Modern psychology has also struggled to understand hypochondria. “The position of hypochondria is still suspended in darkness,” Freud complained in a 1909 lecture. Hypochondria, for him and the psychoanalysts who followed (including my own), is the product of an ego stuck like a car in the mud, expending its energies uselessly, in self-reinforcing frustration—what Hegel had called earlier the “inability to come out of oneself.”

The imagery of darkness is revealing, though not exactly in the way Freud intended. As children, we know nothing of what is inside, and so we often posit the body’s inaccessibility as a darkness, albeit one that routinely emits farts, tears, and blood. Later, that darkness is filled with guts, and, later yet, the guts become differentiated into organs with the simplistic functions we learn about in seventh-grade biology class: the liver filters, the heart pumps, the spleen, well, surely it does something. Healthy adults trust that organs will continue doing what they should like diligent workers in need of minimal supervision. The system may occasionally sputter, but that is why we have the general practitioner.

The hypochondriac never develops that trust in the body’s efficient functioning. For him, it remains what it was from the start, an unknowable, opaque mess to which he is hopelessly bound, like a travelling partner whom he never asked for and, in fact, would jettison if he only could. The darkness of childhood not only refuses to dissipate but grows fecund with cancers, aneurysms, ulcers, deposits. It becomes the oceanic depths from which the shark hungrily swims towards the surface.

This leads to a state of perpetual bewilderment, one described by the novelist Hilary Mantel as a single unanswerable question: “What in God’s name is going on in there?” The answer, I am afraid—have been afraid, ever since a doctor friend of my parents let me look at his medical books when I was a little boy—is written on that pen.

It doesn’t help that we now live in what Barbara Ehrenreich has denounced as “ribbon culture” in “Bright-sided: How Positive Thinking Is Undermining America,” her book about breast cancer. What started with the red AIDS ribbon, in 1991, as well as a pink one for breast cancer that same year, has evolved into a full spectrum of colors, commemorating everything from autism (multicolored puzzle pieces) to celiac disease (lime green). Alertness campaigns tell us to check suspicious moles and get fibroids removed. Yet we should not, like a Woody Allen character, run to the neurologist after every migraine. Unless, of course, that migraine is accompanied by occluded vision and ringing in the ears. Then you really should see someone.

Allen is, in many ways, the ur-hypochondriac, as he has the quick intelligence sometimes associated with the disease. Those who are curious about their bodies are often curious about other things, too, which is probably why so many artists have been hypochondriacs: the ingenuity of thinking up of new ways to die can be channelled into more productive enterprise. In “The Hypochondriacs: Nine Tormented Lives,” Brian Dillon provides pithy accounts of some of history’s most famous hypos: Charles Darwin, Andy Warhol, James Boswell, Charlotte Brontë and Florence Nightingale. Noting that these extraordinary individuals suffered from a condition that put them in the same league, psychologically, as the supremely effete George Costanza, Dillon writes romantically, though not inaccurately, “Hypochondria…was a kind of calling, almost a vocation, that structured a life, or the productive portion of a life. At once crippled and cosseted by fear, the hypochondriac suffered in order to work, to write or to discover in solitude.” If we are to believe Dillon, hypochondria is the steam that powered the engines of creativity.

I have found hypochondria to be rather dull and time-consuming. Searching online for pictures of enlarged lymph nodes has all the furtive desperation of looking at pornography without any of the gratification. And the eternal watchfulness, the constant inspecting until the skin grows red and the mind weary, drains both time and attention, turning you into a solipsistic bore. Cowards may suffer a thousand deaths before they die; a hypochondriac suffers that many in a single afternoon, and, if you give us the time of day, we will tell you about every single one. We simply cannot help it, unable to extricate ourselves from a bathetic cycle of fear and reassurance. Listen to us, pity us, do not discount what we fear. Please.

As psychology has shifted from Freud to neurons, the practice has sought to make more rigorously scientific its understanding of hypochondria, which now affects perhaps as much as five per cent of the American population and siphons an estimated billions (some put the number at a depressing yet unsurprising twenty billion) annually in unnecessary medical visits. In the upcoming fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, universally used to diagnose mental illness, “hypochondria” will be replaced with “Complex Somatic Symptom Disorder,” so that it can be more easily identified and, presumably, treated with either therapy or medication.