My dog was injured by a vehicle out in the road years ago. We took him to the vet for x rays & he had a fracture in his right leg. We ended up taking him home without any kind of pain medicine. We put him in the barn on a thick layer of straw. I could hear him whine with pain. He wasn't given any pain medicine because the vet didn't want him up running around. He felt it was necessary for my dog to lay & be still so the healing would take place. My dog did stay down & took a lot of attention making sure he ate, drank, & was as comfortable as possible. Luckily it was a warm time of year. Maybe your dogs system is shocked right now & drinking the water will keep him hydrated. What a stressful time this must be for you & him.