I usually play like that in games like Crysis or CoD4 or NFS, anyways not for 20 hours but I always keep goodies in handy. A 2L bottle of Pepsi Twist, some nachos, sandwiches, some candy bars, and the occasional beer. And the toilet is reserved as top-priority during the gaming time, so if I need to empty the tank noone gets in my way. The most I've ever stayed was 14 hours. But WTF, sitting at your PC playing WoW until you start bleeding from your orifices, foaming at the mouth and getting foggy eyes? That's not normal.