If Rusty is acting fine any other time, then the only thing I could think of is, he is lazy or there is a tack problem. You said he was shaking his head, might be a tooth/bit problem.
He wasn't really "shaking" his head, more like swinging it from side to side slowly. It was more "I don't want to do this,,,groan,,, type swing of the head:)
I think he has just gotten lazy. Been off too long.
Becky