Sleep is the best thing for you I think. When you're sleeping, you're body's not doing much except working on killing the cold.
For some reason though, I only get sick about once a year, and it's usually a minor runny nose and sneezing or something. That's crazy because of the amount of unhealthy stuff and lack of sleep I get (for example, yesterday I was up for nearly 40 hours, then came home and slept for a little over 17 hours straight). You'd think I'd live sick. heh