Just go away.
I usually am fine when people ask me what's wrong. I mean, I live in a society where it's not okay to be introverted. Apparently, it's wrong to not be social, or something HAS to be wrong with you if you aren't contributing somehow to the conversation. I don't remember anyone telling me this at birth, which is unfortunate, because I would have argued against it.
Or tried to, anyways.
I would rather be alone with my thoughts. Just soak in them because I can focus better (however contradicting that may seem). I listen to my music loud when I'm in public, but it's just barely on when I'm alone - I just like to be in my zen mode. Me, myself, my words. Friends are welcome always, but know that when I'm quiet, I truly am okay. When I have a sad face, you can hug me, give me food, whatever. But don't think something is wrong, or so bad I can't deal with it on my own.
(That was the strangest rant I have ever gone on :/)