Why do I have the urge to mutiliate myself?

At its weakest I slash my arms and legs with a razor, pair of scissors or a knife. However I really want to get my chainsaw and cut my hand off. I want to cut all my fingers off first. I want to cook one of my fingers in the oven because I want to cannibal myself. I want to know what human flesh tastes like aswell so I want to cut some of my fat off (I am quite big and fat). Why do I feel this way? Is it normal?