I'm experiencing the same exact thing you are. I'm a pretty shy person, close to severely introverted, but there's something inside me that tells me I
have to act, or at least try to learn. I heard somewhere that people who are the shyest tend to give the best performances, and here's my little theory on it (that Robert de Niro quote mentioned earlier kind of relates to this):
Shy people almost never get the chance to fully express themselves, so instead they tend to bottle it up because they're scared of other peoples' reactions;
Will they laugh?
Will they hate me for what I just said?
Did I say that right?
We tend to suppress those urges for self-expression, so I think we view acting as an outlet for all of that accumulated energy. We use that energy in the roles and characters that we take on, and all the while, subconsciously or not, we stop worrying about what other people might think because, if we look stupid, or dumb, or awkward, we can always just blame it on the character that we're playing. So that urge to express ourselves, after being suppressed for so long, is poured into our performances, giving it something passionate.
But that's just for me, anyway. I don't know if you feel the same way or not, but that's just how I think shyness creates a passion to act, to self-express. I think acting relies heavily on internal thinking and contemplation, and that's what shy people do best, from what I've read. Anyway, I'm glad there's someone out there that is in the same state of mind as I am, in terms of wanting to act. I've never taken an acting class (I'm planning on it though, just as soon as I get my schedule straightened out), but I'm pretty sure making a fool of yourself in front of a bunch of people is expected when it comes to acting; just to remember to blame it on the character you're playing.
Good luck to you!