Is it normal to fantasize about sexually assaulting people constantly?

I've been plagued with violent fantasies for many years. Being in my early 20s, I'm barely holding my head above water. Shit job, shit home, shit for friends.. I feel like the penalty for living my fantasies isn't nearly as deplorable as it should be to me. I used to dream about sex, finally laying with my best friend who I'd been chasing for years or maybe that ex girlfriend comes around to relive some of the good times we had. Now I dream about rape, and sadism. Rape excites me, more than anything else. Now I dream about pain, I have the urge to do incredibly cruel things to people. A random stranger.. a close friend. Hellraiser gets me hard, SAW made me smile in bliss, 70's women in prison movies arouse me highly. I have a submissive in my life, she willingly lets me explore little bits of my sadistic side with her, but I never get close to living the dreams.