How long has it been since you saw him last? My cat, Thomas, lost weight over a weekend, literally. Sometimes when it's something serious, it can happen fast. It turned out that he has cancer, and unfortunately was given a very grim outlook and put on steriods for the pain and to increase his appetite. Well, it turns out he's supercat, and he's outlived the dr's expectations by 6 months already. In fact, I took him in for a follow-up ultrasound in March, and his two of his three tumors had shrunk and the third one had completely disappeared.
On the other hand, he once lost weight fairly quickly b/c he'd eaten a large part of a plastic bag (he likes to eat plastic bags, certain shower curtains, etc, so we have to keep that stuff away from him). The vet ran all kinds of tests and kept him overnight to run more tests, b/c nothing seemed out of place. The next morning when they got to work, he had a hairball of plastic in his pen. They called and said they'd found the problem.
In fact, when the dr called about the "mass" he found with cancer (you could feel the biggest tumor), I asked if he was sure it wasn't plastic. This was a different vet than the one who dealt with the plastic, so I'm sure he was puzzled by that question!
My family had a cat that showed up at our house when I was 17. She was a little dim. My dad insisted that their cats be mostly outdoor animals (inside to eat and, of course, whenever he wasn't around... lol), and she wandered off one day. She came back a couple of weeks later, I believe, very skinny and looking awful. It was very strange.
So you never know. Hopefully the mass is just something he hasn't passed yet. Did they recommend cat laxative, like the stuff you use to get them to pass hairballs instead of throwing them up?
Hang in there, Ozone.
