I'm convinced Fibromyalgia should fall under this category. After all, you can't see,smell,feel,or taste it. It shows up under no imaging technique. You can't really test for it; there is a "criterion" of more than a certain number of trigger points being positive, but in my experience, I can touch literally anywhere (elbows, forehead, etc.) on a pt. claiming to have fibromyalgia, and they will state they are tender there. So it is a useless test.
Shouldn't one be suspicious of a condition that (a) is only there because the patient says its there (b) cannot be verified by any known test (c) persists for whatever duration the patient says it persists for; no way of objectively telling, and (d) allows a patient to apply for disability, workers' comp, and pain meds?
For those who point to the immense number of fibromyalgia sites and support groups on the Internet as proof there must be something to it, I counter that there are thousands of sites devoted to UFO sightings also. Doesn't make it real.
What is real, for the patient and her familiy, is the suffering. However, I truly believe they will more likely find effective treatment by regarding it as the psychosomatic disorder it is, and seeing a psychiatrist, rather than vainly search for medical cures for a nonexistent physical/anatomic cause.