I'm the same way. I think most people would be surprised to see the true way I feel about things. It's strange because I don't try to hide it, it's just like there is no connection between my exterior response and interior feelings.
Writing this even made me recall a rather funny memory. I can remember receiving a gift from my grandparents one Christmas and saying "Oh, thanks," in a rather monotone voice. I quickly qualified that with, "It may not sound like I like this present, but I really did. Thanks." I feel like such a robot, when I'm really not at all.
"They had to laugh, otherwise it would be too terrifying." -Bukowski