Guess we don\'t want the game to be too realistic...
I made an equation for you

Playing = Having a good time
Being ill = Not having a good time
Playing + Being ill = Having a good time + Not having a good time
Playing + Being ill = 0
Playing = Not Being ill
My first equation came out \"Playing = Being ill\" but I knew that couldn\'t be right

We could have a cough or something though which wouldn\'t affect to our stats or anything but to our appearance... Just a thought.