If I feel well enough to be in the office, I ride regardless of how I'm feeling. I'm just never that sick. Once I started feeling pretty nauseous after I got to work (stomach bug was rolling through the family) and I left later that morning to go home. I ended up throwing up in the bushes on the side of the road and then resuming my commute. I was weak and kind of shaky, but I got home ok. I take the approach that sometimes you just have to push your body to see what you can do.