Is our new ferret sick?

He is a few months old. Was litter box trained almost immediatly. Recently stopped using the boxes so we were re-training him assuming he was just showing his butt. Now all of a sudden he has been having really runny stools, and wont even get up! He will lay right where he was laying, fart, and have a runny bowel movement all over himself! He was eating ok until a few hours ago and now hasnt touched his food or water, and is sleeping in his litter box. Can anyone tell me whats going on with him? He seems pretty lethargic right now but was playing fine earlier. Keep in mind hes been caged for a bit since having these nasty runny stools and not using the boxes. Im worried about our Little Dude!