Yeah I wouldn't really suggest doing to much exercise either. As the above person said, just go for a walk if you really don't want to be sitting around. And try not to worry, your fitness or skills shouldnt drop to much over a few weeks.
I'd try to put more concern into getting better as best you can. Eat some good nutritious meals, take a good multi vitamin and a few vitamin c tablets each day. I had a few weeks off from the gym not to long ago as I had a bad flu, and I found that returning after not doing much was actually very good for me. It all feels fresh again & your brain is really switched on to fine tune all your skills. A break off every now and then whether your sick or not actually helps progress...
Oh yeah, try to watch a lot of fights & things like that so when you hit the gym again your really pumped to make up for the time you've spent out of the gym.