I subbed a class for someone who was out sick this morning. It was an algebra class and the second day the prof was out, so I was asked to try to actually teach something. Unfortunately, I never found out what he was doing in class, so I ended up having to ad lib something about graphs of transformations. (You know, a little algebra improv. "Now pretend you're a function translated to the left two units! OK, now you're getting stretched, s-t-r-e-t-c-h-e-d... AAAAANNNNND freeze! Reflect about the y-axis!" Well, something like that, anyway. Only less entertaining.)
After class I had several students asking me more about who I was and if I taught various courses. (And not in the "Ye gods, I must be sure of who you are so as to avoid scheduling you at all costs, you weirdo!" way, either. They seemed to like me.) This is always a little weird, because usually my own students aren't that crazy about me. They would probably like someone else who came in to sub for me and did some free-form math jazz better. I can just imagine my students all crowding around the other prof, asking if he ever taught the next course they needed to take.
This is why I don't take sick days.