i haven't experienced that exact thing, although i used to self harm as a way to relieve anger. now, sometimes when i think of something i really don't want to think about (usually a memory that makes me ashamed), i get the urge to hit myself on the head - like to make it "go away". now i anticipate that feeling though and mostly can control it, or just put my hands on my head. but the compulsion - it's like a reflex - is strong.