I'm not sure. I've done a lot of reading about this condition, but I have brain fog, deluxe edition, so I can't remember what I learned where. I have seen people link the condition to mono (I had a very severe case when I was in college). Ever since that time, any time I would get overly tired, I would have a feverish feeling. Of course, if I took my temp, it would be normal or lower than normal. In recent years, I've deduced that "normal" for me - or any time when I feel okay, I run about 97.4. Anything much over that and I start feeling bad. In the past month or so, my fever has been almost constant and it has been miserable. Can't really link it to any exertion or stress.
But I've wandered way off topic. I don't think it really proves anything, but I was a gym junkie. One of my great joys was that I would frequently be lifting heavier than some of the men in the gym. But then I got slower and weaker until I had a major health crisis, and I just never recovered.
I've read that ME/CFS can be triggered by any major physical, mental or emotional stress. I've read that having mononeucleosis can lead to ME/CFS later in life. I've also been told that having an abusive childhood sets you up for ME/CFS later in life. There is all kinds of speculation out there, and I'm glad that it seems, at least, that the medical profession is beginning to take the condition seriously and it's being studied. But I'm the trifecta: abusive mother, mono in college, infarct in my fifties, and now I can add weight-lifter/gym rat as another possible contributing factor. I can't get qualified for disability, but I sure can ring all the bells when it comes to contributing factors!