Hi, my ~7 yr old Sonoran desert tortoise came to me about 3yrs ago. He seemed to be fine until ~1-2 mo ago when he started having problems walking. He would kind of collapse on his left hind leg. I also noticed spending more time sitting in the open in his shell and not deficating as much. Then when I saw him a week ago he was very uncoordinated and could barely walk. The vet said his blood work, stool sample, x-rays negative. He was dehydrated. Any ideas on what's wrong? Vet said we'll likely have to put in a feeding tube if he doesn't start eating more. She gave me antibiotics to inject.