Please don't let it freak you out! I'm so sorry...that wasn't my intent! Just something to be aware of. My cat has some abdominal inflammation due to a small mass that is managed by lasix and prednisone. No diarrhea. I am not a vet, but I suspect it is food related.
It sounds like the cat may have some fluid buildup. Is he side breathing or abdomen breathing? Inhaling more than exhaling? I have had 2 cats with the same issue and the first indication that I had was that they stopped eating the dry food. It takes more effort to eat dry food, and when there is...