Daisy was sick like that a few weeks back. Most likely he is hiding because he doesn't feel well and that's his way of trying to feel better. I know when I don't feel well, I just want to be left alone. If he's keeping water down that is good. I would give him a tiny bit of plain white rice and boiled chicken. I started Daisy out with 1tsp and waited 30 to 45 minutes and gave a little more if she kept that down. Try not to worry, I'm sure Casie will be fine.