The CDC statement was almost certainly intended as a rebuke of people like Michael Sharpe. Back in the 1980s, when the professor emeritus of psychological medicine at Oxford was still a junior researcher, an infectious-disease colleague had grown flummoxed by patients with unexplained exhaustion and pain. Sharpe spent months in that clinic, meeting with and listening to the patients, taking full histories, and reviewing the standard lab tests they’d received. And while he couldn’t say for certain why they were still so sick, he did notice that the ones suffering the most tended to be intensely focused on their symptoms, distressed about not getting better, and very worried about doing anything to make their ailments worse. Some were so anguished that it overwhelmed them. They even avoided things they’d once enjoyed. “That’s how I got involved,” he told me. “I’ve always been interested in seeing if we can do things for these patients that medicine can’t. You know, is there any way you can come from another angle here? In this case, some kind of behavioral angle that’s different than just doing lots of blood tests?” When cognitive behavioral therapy seemed to be helping people with other conditions, Sharpe wondered whether it might also help patients whose symptoms, however severe, simply didn’t line up with pathophysiological rules. In one essay, he characterized this as having “illness without disease.”

As it turned out, there were quite a lot of these patients, and Sharpe passed on his passion for treating them to his young neurologist advisees, Jon Stone and Alan Carson. In the 1990s and early 2000s, it was becoming clear that illnesses previously known as hysteria hadn’t simply vanished, sorted into more appropriate diagnostic categories, as Eliot Slater had urged decades earlier. Stone and Carson began to study the symptoms with a neurological lens, conceiving of them as misfiring brain signals rather than a Freudian cry for help. Rebranding hysteria as FND was to reject the notion that the best way to understand functional paralysis was as a subconscious repression of childhood memories. Rather, it was an interruption in the brain processing that facilitates the executive function of your legs—a blip that could be triggered by all sorts of things.

In other words, stress could exacerbate FND, and someone with FND could overfocus on symptoms and essentially turn up their volume, requiring brain processing for actions that should be automatic. As Carson put it to me, the term “functional neurological disorder” should be reserved for neurological symptoms like weakness, seizures, memory loss, or cognitive issues. “Functional symptoms” and “functional disorders” are largely used interchangeably about other parts of the body. Irritable bowel syndrome, for example, is widely theorized to be a functional disorder. Meanwhile, conditions like depression and anxiety frequently include symptoms most people would describe as physical. It’s even possible to have functional and nonfunctional symptoms at the same time. “We wonder why people get confused!” Carson quipped.