Absolutely. Put me in a small group of close friends and I'm happy as can be, and even talk a lot. Put me in a social situation with strangers and I clam up and get antsy. Parties, though sometimes satisfying, are very emotionally draining to me, and I always need some alone time afterward (or time with my wife, who is "inside the fence," as it were, and doesn't trigger my need to be alone at all). I've always been that way. There are some situations where I consciously act against my natural inclinations, notably at Clarion and other writing workshops, where I make a point of putting myself forward and talking to people. That's led to some rewarding friendships, but yeah, the effort makes me tired. My perfect weekend involves staying home with my wife or hanging out with a couple of close friends. Definitely not parties or big group outings. And at parties, yeah, I tend to drink to make social interaction a little more pleasurable.

That said, I don't feel any shame about being that way. I've mostly been pretty comfortable with being an introvert, even hiding away and reading at social gatherings, to the occasional chagrin of my family.