My dog was sick when I got him from the pound -- I've since learned that he has pretty severe separation anxiety and being left by his previous owners upset him so badly that he refused food and was extremely listless and pitiful. He was physically better by the third day, but didn't really "bond" to me for a couple of weeks. We've been together 6 years and he's far and away the best dog I've ever had. Still has separation anxiety, but at least he comes by it honestly!