Why do I always feel numb?

When I'm around other people, I'm the most spontaneous person there is, but it's just an act. Truth is, I feel entirely emotionless. No aggression, no true excitement or happiness, no depression... I never really noticed this lack of true emotion until a couple days ago, when I realized that not only have I been smoking, (cigarettes only) but I burn myself with them when I'm done. And the worst part is, I don't know why. My life's not great but so what right? Nothings perfect. But shouldn't I still feel something?