Is it normal to fantasize that you are being molested?

I have fantasies that I am being molested, rapped, used, violated...these are the types of things I most often think about during masturbation. For example: I'll fantasize I'm at the doctors office and he drugs me and rapes me. Or he touches me sexually while examining me. Or I'll fantasize that I am kidnapped and used for sex by many men. My last boyfriend was the best sex I ever had because he would role play these fantisies with me. ie: Tie belts around my neck and pretend force me to blow him or have sex with him. Is this in any way normal?