Most people think that when they are sick that it is okay for them to work out to sweat out the sickness and the toxins. While it may be good to sweat, it is not good to exercise and try to be active. People that are sick should be advised to stay in bed. When someone gets sick, their body is internally fighting bacteria.
This is a way for their body to tell them that they need to take a break and get some rest. One day without exercise will do no harm. It is actually good to take days of rest sometimes so that the body has time to recooperate itself.