Why Does My Mind Go There?

I am a runner, compete in marathons regularly and put in about a hundred miles a week some times when preparing for one. I run mainly in one of the state parks by my house, it has some many trails thru it and i can easily go fifteen miles without worrying about vehicles. Whenever I am there I fantasize about being attacked and a couple of men making me have sex with them, even tying me up for it using duct tape or rope. I have passed men on the trails and even had a few run with me for a while, the whole time I am just waiting for them to grab me and strip me naked. I have no idea why I think about it so much, it has never happened to me, not even a close call where I thought something was out of control. I was thinking about it and thought maybe it is because I have always had pretty vanilla sex with my husband and boyfriends over the years, think the craziest thing that has ever happened was a boyfriend put me on the kitchen counter one time and pleasured me then bent me over the end of the couch for him to finish. I know if something like that really happened to me I would be just terrified and I seriously wonder what is wrong with my brain some days.