I can't really offer a lot with regard to this. The one thing I can tell you from personal experience is that, while hitting your head may not do a lot of damage short-term, over the long haul it is a very bad idea!

I stopped when I realized I had done permanent non-treatable harm to myself. I know you wrote you don't trust therapists (or psychiatrists.) I'm not a fan either. But talking through what is going on inside you that is driving you to do this to yourself may be your best chance of putting it to rest once and for all. I hope you can. My best wishes to you...