It's not always about feeling awkward; sometimes I literally have nothing to say and my mind is just blank, especially when tired.
I've always felt pressured to talk for fear of being labeled quiet, but as I've gotten a little older I've come to realize that isn't the terrible thing American culture makes it out to be. I've known lots of wonderful "quiet" people. And honestly... why talk just to talk? Nothing wrong with it per se, but nothing wrong with not feeling it serves any purpose for you. Quiet does not necessarily mean weak, boring, timid, etc., as many seem to think.