It was definitely the caffeine. For example, a can of Diet Coke was just as bad. I also know from experience with other stimulants that I was just extremely sensitive to stimulants in general (and so is my mother, and so is my daughter).
I guess I would say that I'm interested in a desultory way, but without urgency.
I've achieved a good adaptation to it, and my life proceeds mostly as if I didn't have it now, as long as I observe some rules: regular schedule, good nutrition, regular low-impact exercise. (If my exercise gets too high-impact then I cross into the kind of fatigue I cannot easily recover from.)
I do follow science and medical news related to it. The present state of affairs as I currently understand it is that it's still a syndrome rather than a disease, which basically means it's a big bag of symptoms without an agreed-upon underlying cause or mechanism. There's some evidence that ties it somehow to the Epstein-Barr virus (and, perhaps coincidentally, one of my kids had mononucleosis in the months before I developed the syndrome). There's also some evidence that suggests that susceptibility to it is heritable. Some researchers have hypothesized that it's an epigenetic disorder--that is, a genetic disease that is activated by an environmental trigger (such as a viral infection--a large fraction of CFS cases start with a viral infection).
Someone published some work that claims that folks with CFS have distinctively abnormal calcium metabolism, which might account for the difficulty recovering from fatigue.
There are still some people who think it's psychosomatic, or mostly psychosomatic, too.
That's about as much as I remember off the top of my head. As I say, I'm interested, but not urgently so. I seem to have found my accommodation.
Not anymore, though; not since I developed CFS.