Met with our vet today (been seeing him for 10 years so he knows Shaggy). Shaggy is getting ready to shed on top of this so we are waiting to see what happens once he completes his process. No outwards signs of tumors or broken bones, breathing fine, and heart sounds good. Vet doesn't believe Shaggy is reacting in a painful way. Vet spoke about strange behaviors with sheds and season changes so Shaggy could just be going through something. He could have also tweaked a muscle or strained himself moving around....
So lots of possibilities but Dr doesn't see any imminent issues so while I wait for a shed, I'll be documenting behaviors and keeping up with normal routines. If Shaggy isn't back to normal, we will proceeded with xrays and whatnot.
I'll try to get on and update as we go!