Yup, the forced reevaluation of physical activity is hard. Ballet for me wasn't just something I did, it was part of who I was. When I got fibromyalgia, I was taking 12 ballet classes a week and in the best shape of my life. It took me a long time to find something else. Because fibromyalgia behaves differently in each person, there's no easy way to sort through it. The twisting of body parts and the hard pushing of one set of muscles against another set that is part of ballet created major muscle pain for me that spiraled out of control and stayed there. I did try going back to class several times when I felt better, and each time, it re-started the pain, so I learned I could not do that anymore. It was pretty hard for me to give up and I was very angry about it for a long time. You would think that cycling might not work because of the upper-middle back and arm use, but it has, as long as I am careful not to place too much weight on my arms for a very long period of time--so bike fit is important for me.
I guess I am saying: DON'T give up the athlete part of you. Just know it'll take some aggressive analysis on your part to figure out how being an athlete can be reconfigured for you so that you can still do it well and not have it make you feel sick.
And, by the way, my fibromyalgia started with constant headaches and weird visual symptoms. It's a REALLY annoying syndrome.
I think many of these are probably related underneath--fibromyalgia, celiac, rheumatoid arthritis, other autoimmune-type reactions.
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks