That's the problem with all kinds of illnesses from chronic fatigue to schizophrenia that are diagnosed based on a set of symptoms rather than on what is causing the set of symptoms. A very good book on the topic is which includes tests for ruling things out when diagnosed with fibromyalgia, and chronic fatigue are "Your Symptoms are Real" by Benjamin Natelson.

I agree about the testing.

The diagnosis is a step in the right direction from just a few years ago... after all, the same set of symptoms used be called "in your head", hypochondria, laziness, mental illness, etc. At least now they call it something medical and treat it as "it's real, and medical, but we don't yet know what it is". Of course, if they ran tests they might figure out what is causing at least some of the cases.