I've mentioned that there are a lot of people who are misdiagnosed because doctors aren't clear on what CFS is, what symptoms rule it out, what else it might be.
CFIDS.org provides the following list of other conditions with similar symptoms.
Conditions that share some symptoms with CFS
Irritable bowel syndrome
Poliomyelitis/post polio syndrome
Exposure to toxic chemicals, heavy metals, pesticides
Each and every one of these other diseases needs to be ruled out before a CFS diagnosis can be given. CFS is not just "chronic fatigue" -- there are a lot of other medical conditions that cause chronic fatigue.
It's the constellation of other symptoms that make it CFS.
For example, CFS and MS have many symptoms in common, including fatigue and neurological problems, but double vision is one that can be used to definitively say it's MS; with CFS, it's more likely that your vision will be blurry instead. A lot of CFS patients were diagnosed with "atypical MS". A CFS specialist can tell you the difference, even if your PCP doesn't know.
An activist in the UK tells me that a lot of people there were wrongly diagnosed with CFS when what they actually had was Lyme or Brucellosis. As a result of not getting the proper treatment for what they do have, they got much worse. With many of these infections, including CFS, time is of the essence. The longer you're allowed to deteriorate with improper treatment, the longer it will take to recover (if at all; the damage may be too severe by the time you're properly diagnosed).
In my case, it's especially irksome because the doctors didn't need to MAKE a diagnosis. They were told what the diagnosis was, and that it had been made by a virologist and confirmed by a rheumatologist. All they had to do was give me the right pills. They did not have to exercise a single brain cell, because I even told them what to give me. They gave me everything else instead, then blamed me because I wasn't getting better. Subsequent doctors have been totally confused, "what would it have hurt?" for them to humor me with some sleeping pills while waiting for the blood test results.
The only answer I have for that is, it would have hurt their egos to have to admit that the patient knew more than they did. I'm permanently disabled, but the doctors' egos are intact.
And, no, that does not give me warm fuzzies to know that they feel better about themselves.