What does my face say?

Do your facial expressions or your body language actually mirror what you are thinking or your state of mind?
I'm not so sure of this. Just the other day, a friend told me that my expressions are very reactive, they give away exactly what I am thinking. It's true, many people have told me the smae thing. Butt that is slightly disconcerting. I'm not too cool about the idea of people having a glimpse into my innermost thoughts. Heck, that obviates any need of telepathy!!!
But I thought a bit more about that, and I agree I am very expressive. But, I pointed this out to my friend, and she had to agree that I am very good at controlling my emotions. I never show what exactly is cooking in my mind, to anybody. Not my parents, not my friends (ok, at times to my brother, and my best friend), but to no one except myself.
When I told this to another friend, he believes this is'nt something to be too happy about. This is going to lead stuff to fester in my mind alone, and yeah, not all problems can be solved alone. He suggests I really need to open up, to someone. For once, I'm gonna take his advice, atleast I will try...