You're right, that's not the way I'm using it at all. Far from it. I have never heard the term "designer illness" used to mean "made up". Not sure where that would come from.
What I am saying is that this illness is unique to each of us who has CFS. It is custom-tailored, so to speak, to every person who suffers from it. There is such a wide range of symptoms, which makes diagnosis and treatment even harder.