This disease is so odd, the way it evolves over time. For the first three years of ME/CFS, I would crash if I drank coffee. Even decaf. And believe you me, I tried many many times, such is my love of coffee. I kept thinking, "oh, the last time was a fluke. I just happened to crash right after drinking coffee It will be different this time." It took about 8 to 10 experiments before I finally accepted that I couldn't drink coffee.
Recently, I've tried it again, starting with decaf, and all of a sudden I can drink it again without crashing. I don't know if that means I should, but I just can't emphasize enough how nice it is to know that I can if I want... at least occasionally.
[1/27/15 update: I am no longer able to drink coffee. That only lasted about 5 months.]
On the bad side of things, that aching in my kidneys that had gone away for so long is starting to come back again.
That's how it seems to go with ME/CFS for me ever since I got it. One issue will resolve itself, but another will arise. Often it feels like a zero sum game.