Does anyone know anything about sinusitis? I took my almost-two year old cat to the vet after she sneezed and wasn't drinking water as well as seemed mildly lethargic. The vet did a check up and said that she didn't have a fever, her eyes and nose weren't crusty, and since she was still eating (albeit less) and she was still using the litterbox she didn't seem to have anything wrong with her. He thought maybe sinusitis. This was Monday. She has been eating a/d wet food as well as her Friskies wet food as per vet instructions and has started playing more. He gave her an IV of water. She seems 85% better. But I'm still not exactly clear as to what sinusitis is/entails. Any thoughts?