That is quite a behavior change and would call for a thorough vet exam. Aso check out Rabies vaccinosis. (PM me if you want the details). I lost a dog to this. In the meantime avoid others to put pressure on him.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015