I agree with all the comments on ulcers, and have also seen a quick turn around with omeprazole in these horses.
Did you move him to re-hab him? I assume if he is only getting light turn out and stall rest he is on no or very little concentrated feed. If not that is certainly a change I would make. If he has trouble keeping weight I would use beet pulp or rice bran to keep the weight on without him coming out of his skin. His behavior may have more to due with being cooped up than it does with the move.
I have also had great results with Quiessence in horses that just don’t seem to be able get over anxieties for a variety of reasons.