Mimi, I've found that the older I get, the longer it takes me to recover from both exercise and being sick. Last winter I had bronchitis in Feb. and it was the end of March before I felt myself. Also, I think it could be related to the fibro.
Try the walking before you do anything on the bike or spin; I've set myself back too many times than I care to remember by trying to get out on the bike before I should have.

Robyn