I had a run-in with an NHS person a few weeks ago about CFS vs ME. I was trying to argue that it was no good her trying to get me to do GET because the evidence was based on people with an ill-defined fatigue syndrome (CFS, probably Oxford criteria) rather than what I'd got (the neuro-immune disease ME). I'm seeing this person again (last time, I hope) next week and would like to be better prepared. My impression is that the 24-48 hour delay in profound fatigue following the activity that causes it is considered as a cardinal symptom (i.e. you have to have it or you don't get the diagnosis) of ME. My questions: 1. Is it delayed fatigue rather than PEM that's the cardinal symptom? Am I confusing two things? I'm assuming PEM = feeling not just tired but flu-ish after exertion, but not necessarily delayed. 2. Where have I got delayed fatigue as a cardinal symptom from? Is it the Canadian Criteria? 3. What's the history of delayed fatigue being adopted as a cardinal symptom? How does something get chosen by researchers to be a cardinal symptom and rejected by others - that is, what's my argument for saying that I have "proper ME" rather than just unexplained fatigue, because my fatigue is delayed? 4. Is there any evidence on what proportion of NHS-defined CFS patients have ME? Embarrassed not to know this stuff already! Would be very grateful for references/links to any academic papers, including the latest systematic review the NHS is basing its training of personnel on.