I personally do not think the difference between CFS and ME can be based on severity and I would assume there would be many others who do not think that either. "CFS" can be being caused by so many different things, so many missed other illnesses. Some of them just as severe as ME so it is possible to have one who has a CFS diagnoses who may be in fact be sicker then another person who has a ME diagnosis. I think its a case by case thing. The difference I see is in the "symptom complex", the amount of different systems of the body affected, the actual grouping of the symptoms (with post exertional P.E.N.E aiding the diagnoses). I do believe its true thou that "many" ME cases are worst then "most" CFS ones but that simply isnt always the case hence ME and CFS can never be separated on severity. You can get a bedridden CFS person who does not have ME.