When our boy had panosteitis this is exactly how he acted...he did not really present with the classic limping. He just wanted to hide and sleep. He was about the same age as yours as I recall (this was in the 1980's). Maybe ask the vet about that?
Hope he feels better soon, and please keep us posted.
Soli Deo Gloria.-used by
Bach and Handel to sign their work-
Because when I see a Horse cantering
for the pure joy of it, or a Dog working
with their beloved person, I think to myself,
"Look what God did".