Jodi-Hummingbird, I am sorry about your M.E. but those who have not read this book (I didn't find it very good by the way, not a typical Ruth Rendell) could easily be misled by your piece.
The point is that Irene Litton does not have M.E. (see page 11 in my copy). She is a hypochondriac who only THINKS she has arthitis,scoliosis,M.E. and early Parkinson's. Ruth Rendell is not saying M.E. is imaginary, but that the character imagines she has it. Before attacking her Jodi you should have re-read that paragraph - but maybe your pain got in the way.