Please check out the discussion on megaesophagus. My cat had the same symptoms, and that's what it was. The vet can determine this by doing an x-ray with barium.

Our 13 year old cat has just (last Monday) been diagnosed with megaesophagus. He lost a lot of weight before we figured out what was going on. I like the idea from HottKoko. I'd love to see a pic of the feeding set up. Our old boy is having probl...