Hmm. Could you get him in any sooner at another vets office? Does he go outside unsupervised or is there even a slight chance he could have gotten out?

I ask because this sounds like a less severe version of what my RB kitty Tier had. He was completely indoors his whole life. One day, we came home and he was slightly limping. The next day, he couldn't use his back end at all. There's a lot more to all the things that were wrong (PM me if you'd like to know, I don't want to hijack your thread). I am not entirely sure what the vet called this because I was in a daze. We had to send him to the RB the day after he lost the ability to use his legs, so I stress the importance of going to see a vet ASAP because you might be able to save your baby with surgery or, if it's less severe, then meds and therapy (i think!). So check around!

I hope he gets to feeling better soon!