Resting when sick is beneficial because it allows the body's resources to be fully devoted to recovery from infection.

“Because under those conditions, what you really want to do is slow your circulation down, probably find and take a little walks or something provided you're not doubled over in bed and vomiting, and things like that. A little bit of movement, probably good to circulate your blood. But in general, the advice that you get to rest when you're sick and not push yourself, that's really good advice because you want all of your body's resources to be devoted to getting over that infection.”