Illness narratives usually have startling beginnings—the fall at the supermarket, the lump discovered in the abdomen, the doctor’s call. Not mine. I got sick the way Hemingway says you go broke: “gradually and then suddenly.” One way to tell the story is to say that I was ill for a long time—at least half a dozen years—before any doctor I saw believed I had a disease. Another is to say that it took hold in 2009, the stressful year after my mother died, when a debilitating fatigue overcame me, my lymph nodes ached for months, and a test suggested that I had recently had Epstein-Barr virus. Still another way is to say that it began in February of 2012, on a windy beach in Vietnam; my boyfriend and I were reading by the water when I noticed a rash on my inner arm—seven or eight vibrantly red bumps. At home in New York, three days later, I had a low fever. For weeks, I drifted along in a flulike malaise that I thought was protracted jet lag. I began getting headaches and feeling dizzy when I ate. At talks I gave, I found myself forgetting words. I kept reversing phrases—saying things like “I’ll meet you at the cooler water.”

One morning in March, I sat down at my desk to work, and found I could no longer write or read; my brain seemed enveloped in a thick gray fog. I wondered if it was a result of too much Internet surfing, and a lack of will power. I wondered if I was depressed. But I wanted to work. I didn’t feel apathy, only a weird sense that my mind and my body weren’t synched. Was I going mad? Then I started to think about the curious symptoms I’d had on and off for years: hives, migraines, terrible fatigue, a buzzing in my throat, numbness in my feet, and, most recently, three viruses (cytomegalovirus, which kept recurring, as well as parvovirus and Epstein-Barr).

My internist did some blood work, and called a few days later. “You’re fine—just a little anemic,” he said reassuringly. For years, doctors had been telling me I was a little anemic, or a bit Vitamin D deficient. But now I was sure that something else was going on.

That weekend, on a crisp spring evening in the West Village, I went to see a movie with a group of friends. Afterward, as we headed for a drink, I began to feel shivery and shaky. I begged off. “Are you all right?” one of them e-mailed the next day. “You seem really run down.” I was sitting at my desk, looking at a photograph of myself as a teen-ager on a tall beachside dune playing with the family dog, a handsome black malamute mix. A strong wind had turned my hair into streamers. I couldn’t remember when I last felt that alive.

I called a doctor at Weill Cornell who specializes in women’s health, and made an appointment. As I described my symptoms and my family history—which included rheumatoid arthritis, ulcerative colitis, and thyroid conditions—she said, “I can tell you now, before I even see your labs, I am highly suspicious that you have some kind of autoimmune disease.”

A few days later, she called to say that I had antibodies to my thyroid, a butterfly-shaped gland in the neck that regulates metabolism and energy. My thyroid was being attacked by my immune system—a disease known as autoimmune thyroiditis, though people refer to this form of it as Hashimoto’s. I didn’t worry about the diagnosis; I was just happy to get an answer. Thyroid disease, I had read, is fairly common and treatable. I knew people with it, and they were fine. The doctor told me to take a replacement thyroid hormone and check back in six weeks. By then, I would be feeling better. This was the way medicine worked: tests told you what was wrong, and doctors told you how to fix it.

But I didn’t feel better in six weeks. I felt worse. My blood pressure was alarmingly low. I got excruciating headaches whenever I ate, and one day when I got out of bed I fainted, gashing my arm on a bedside glass. My joints hurt, and I began to have a stinging pain in my back. There was an itching sensation, which would grow in severity, to the point that I felt I was being stabbed by hundreds of fine needles. None of these were usual symptoms of thyroiditis. My friend Gina and I went to get a juice one afternoon—like me, she worked from home—and I got so dizzy that she had to steady me until I could sit. “You have to get better,” she said to me, “whatever that takes.” She looked at me as if I were really sick. Until then, I had half believed—after years of doctors implying as much—that it was all in my head.

When I saw the doctor, she suggested raising my dosage of the hormone. She didn’t have much to say about the headaches and the other symptoms, but she mentioned that many of her patients did better when they avoided wheat. I began to suspect that whatever was wrong with me wasn’t going to be as clear-cut as a germ or a malfunctioning organ.

The truth is, I had no idea what autoimmune disease really was. For years, I’d known that two of my mother’s sisters had rheumatoid arthritis and ulcerative colitis (and my father’s youngest sister had recently learned she had Hashimoto’s). But I didn’t understand that these diseases might somehow be connected. At Christmas, I’d had lunch with three of my mother’s sisters—humorous, unself-pitying Irish-American women in their fifties—at my grandmother’s condo on the Jersey Shore, and they told me that two of my cousins had been feeling inexplicably debilitated. “None of the doctors can figure out what it is,” one said, “but I think it’s thyroid-related.” Another aunt told us that, along with the rheumatoid arthritis she’d had for years, she, too, had recently been given a diagnosis of Hashimoto’s, and both were autoimmune in nature. The third aunt had ulcerative colitis, and told me that a cousin had just been given that diagnosis, too. “They’re all connected,” one of them explained.

In a normal immune response, the body creates antibodies (Y-shaped protein molecules) and white blood cells to fight off viruses and bacteria. Autoimmune disease occurs when, for some reason, the body attacks its own healthy tissue, turning on the very thing it was supposed to protect. This, at least, is the premise: “auto,” or “self,” attack.

From the start, though, the study of autoimmunity has been characterized by uncertainty and error. In 1901, the influential German immunologist Paul Ehrlich argued that autoimmunity couldn’t exist, because the body had what he called a “horror autotoxicus,” or a fear of self-poisoning. Ehrlich’s theory was so fully embraced that doctors stopped exploring the subject for half a century. Then, in the mid-fifties, a young medical student named Noel Rose, who worked with one of Ehrlich’s disciples, Ernest Witebsky, discovered thyroid autoantibodies while studying the immunology of cancer. After he injected an extract of a rabbit’s thyroid protein back into its thyroid, he was startled to find that the rabbit was producing antibodies to itself. What’s more, the rabbit’s lymphocytes (a kind of white blood cell) started to damage its thyroid, just as happens with Hashimoto’s, then known as “a disease of unknown origin.” Rose and, eventually, Witebsky realized that they had stumbled onto something major.