If the animal is caved in, and is showing neurological signs like that, I can only assume malnutrition, dehydration, and possible IBD. The important thing for that animal is to try to get it to eat.

Someone more experienced needs to chime in here, but it definitely sounds like the animal needs food and fast. If it does have IBD which shows odd neurological symptoms, keep it away from other reptiles, and you will probably have to put it down..