I love that quote!
I have/had a sinus thingie that has moved into my chest. Have had it a month. I actually exercise ok but it exhausts me beyond all belief.
So I guess take what we all say then modify it to suit yourself. I have ridden when I didn't feel well and the ride turned out far better than I could have ever imagined. I'm a firm believer in sweating stuff out but you have to make sure that your other obligations (ie work and home) allow you the rest that you need.