If he's drinking to "numb" his emotional state, or drinks because he's stressed, he could be in trouble! I think most of us drank to hide from our "problems" and to numb the pain.
He needs to find another outlet for his stress, etc., like perhaps exercising or going for walks. Drinking never solved anything -- I think we all know that.

And if he continues on like this, he's going to cross that invisible line into problem drinking!
I'd speak to him and tell him your concerns. If he denies he has a problem, then he might JUST be heading for trouble. It doesn't matter how much or how often we drink -- it's what it DOES to us that makes the difference. And snce it changed his personality, and he did things he doesn't normally do, he might be headed for trouble.
Best of luck & God bless. Hugs, Lee