My guess from his symptoms are stroke. He was fine, then went straight down, lying on his chest, lethargic, unable to move much. Then he recovered a little bit then it happened again. We "ruled out" respiratory, etc in Chat...it sounds like it was multiple strokes to me. The ones that take a young perfectly fine rat when you leave in the morning, and leave you with a dead rat in the cage that evening and a lot of "Oh why??!!!"