A quick google search on "why do I feel so empty?" says some stuff about developing emotional detachment as a "protective shield" due to some early trauma. I think this is my case except it's been exasperated by drug abuse..

here's the link: Why do I feel nothing? Emptiness and borderline personality - Counselling Directory I know it says it's about BPD but I think this specific "symptom" or experience can apply to a lot of people.