It's happened to me before (illness with nausea) when at work. I decided to go ahead and ride home. The train leg of my commute had me more anxious than the biking legs. It caught up to me at the train station and I got sick in the bushes there before my train arrived. Nothing I could do about that. I'm just glad it was before I got on the train. I felt better, relatively speaking, but pretty weak the rest of the way home.