I had a coonhound that one day woke up in the morning and was dragging a back leg, then she seemed to walk normal and then a hour later she was dragging it again and then she seemed fine. Then I had them outside and someone walked by and she charged the fence and when I brought her back inside she laid down and then that was it she could not walk at all, both back legs were paralyzed, so off to the vet we went and she said she had a swelling in her spine. She explained it to me if the spine gets damaged in anyway, it becomes inflamed and in turn swells up and will constrict the nerves in the spine and depending on were the swelling is in the spine will affect the back end of the dog, which means the dog has problems moving their back legs because the nerves are constricted. My vet also said it could be something inside her like a tumor that was pushing up on the spine causing the issue as she was 10 years old. Im sure that is not the case with Hector as you had mentioned that he slid into a wall and that could have been the start of it all and then going up and down the stairs and going for walks could have aggravated it to the point it is now.
I would just make him comfy, don't worry about getting him outside but do make sure you have a big pee pee towel cause eventually he will pee laying there and it will be a lot lol, my coonhound wouldn't even pee when I took her outside but eventually she peed inside where she was laying. If he is not drinking , you need to spoon some into his lips if you don't have a syringe , he needs water, I second the broth idea. Also if he will let you I would try and ice the spot that is hot for a few mins at a time. Not much else you can do besides be with him and that may mean sleep beside him , filas are sucks and it may make him a little less stressed out. The night before I had to put Kiva down she cried all night but was less crying when I laid down beside her and just stroked her side and we both fell asleep. Hope it is just a tweaked back and he makes a speedy recovery.
When you talk to the vet ask about a cortisone shot near the injury, they do it for humans not sure if it is recommended for dogs.
Hugs and best wishes from me and Penelope.
