A drastic change in temperature can shock all types of stock. If he went back under the rock on his own, I would just keep checking to see that he is still alive, and see if he survives.
I'm hoping that the LFS
told you to be very careful near this shrimp. They are nicknamed "thumb-splitters" for a reason. Those 2 little clubs on the front of him pack a serious punch!!
When they strike, they create a water cavitation that you can hear, similar to a sonic boom. And believe it or not, can create light, with the force of their strike!! (Nat Geo special). Steer clear of him!!
Best Of luck, hope he comes around for you....fascinating creature.