I am very similar. I typically don't feel comfortable enough to let my guards down, unless I have drank alcohol. I feel like a jerk for having this very stand-offish trait, I really do hate it!

There are sober times that I let my guard down as well though. Those are special times that assure those that I'm with that I really do care about them & that I do enjoy being with them. They get to see me in that different light every now and then...and those are special times for us. Special times that we enjoy looking back upon.