They tend to have sore insides right after surgery. Imani had a hard time after her spay, and really scared me because not only was she not eating, she wasn't drinking, wasn't moving at all, and wasn't sleeping at all either. I finally started giving her syringes full of pedialyte and putting some peanut butter on my finger and sticking it in her mouth after the first 36 hours or so, and by the next day, she was noticeably better. Ice cubes can be a big help in getting fluids into them, if they will take those but still won't get up to get drinks.