Very possible...mothers can do damage like no other, I know all about that, too. Obviously it sounds like you guys have good communication, so hopefully tomorrow you can speak with him further about the events of the night.

I would definitely try and play down any anger you could be feeling by then (at first in the beg. of the discussion...just to see how he reacts, in case he already feels terribly guilty) and focus on the "being worried" side...about him possibly hurting himself, others, DUI, etc...and maybe find out how much he even remembers? Of course sometimes people don't even remember making the decision to drive, which is one of the more worrisome parts.

Then I would definitely try and get down to what is bothering him, since I am guessing something is (amateur psychology here, but since it is the first time ever for this behavior with him, just a guess)...and if it's his parents and he is willing to talk about his mother, I imagine you can figure out if she called again or if he is having strong feelings re: her and is unsure how to deal with them.

I really hope for both of you that this is a one time thing and that your conversation tomorrow will bring some things to light.