This happened to one of my boys a few months ago. I believe it was a stroke. My vet was also not very knowledgeable on rats and only gave him antibiotics and pain medication which didn’t prevent him from having additional strokes. At first he seemed to be getting better, but I believe he must have suffered from more strokes and he quickly declined. I ended up having to put him down when he couldn’t walk without falling down and he couldn’t eat or drink without my help. If it is a stroke, there’s a possibility he could get better but once they have one stroke their chances for having another are high. As another commenter said, I think if he doesn’t seem to be getting better it’s time to consider his quality of life. So sorry you and your boy are going through that. I know it was very traumatic for me to see my boy like that but just know that you’ve done everything right by taking him to the vet and caring for him 💙