Actually, what most people do is lay in bed, and that form of inactivity slows your metabolism and in turn, slows your immune system, as they're both apart of some system with a weird name that I can never remember. Endocrine? maybe... I unno.
It's actually best to be active, do what you would normally do, except get off the couch! it allows your body to remove the infection faster. Also, many of the medications on the market to fight the 'common cold' are for bacteria or some biological infection. When about 90% of the common colds are virus's. So taking cold medications is actually detrimental to your recovery.
Over hydrating can be a bad thing too.
Kadaj
Death is not to be mourned
It's meant to be savored