"For decades, many thought that it was psychosomatic. (My symptoms were so odd that, over the preceding year, I, too, had wondered if I was going crazy.) This sense lingers in popular culture. In the pilot episode of “House,” from 2004, a patient comes to the clinic complaining of C.F.S., and Dr. House successfully treats him with mints from the vending machine. In a standup set in 2007, Ricky Gervais joked about people who say they have C.F.S. because they “don’t feel like going to work.” Today, though, most doctors who study C.F.S. think that its symptoms are caused by a dysfunction of the immune system, which is typically triggered by an infection, such as the Epstein-Barr virus (which causes mono) or viral encephalitis. Still, they don’t understand why, even as most people bounce back from these ailments, a small percentage of them never recover." ... "The dominant theory holds that C.F.S. may not have a single etiology but may instead be a dysfunctional state of the immune system triggered by one of several ailments. Another asserts that C.F.S. is actually an umbrella term for several immune conditions with similar presentations. Ongoing research at Stanford and Columbia focusses on pinpointing the causes of the illness and on developing laboratory tests to diagnose it. But progress remains slow because, though the N.I.H. has now determined that the disease is biological, funding has yet to catch up."