What does it mean when a girl says things like “help” and “I hate you” during sex?

While my girlfriend of three years and I are having sex, she has some strange things that she says during the sex that have me confused. It wasn’t until about a year into the relationship, after we had started making our own “adult movies”, that I noticed that she had a habit of very softly whispering things like “ I hate you” or “help, he’s raping me” while we were having sex. Obviously this was quite a shock to me and, after I finally worked up the courage to finally ask her about it, she was almost as shocked as I was. Now when I say almost, that’s because it almost seemed like she knew about it, but then she still tried to deny that she says these things afterwards while totally disregarding the evidence (our movies). Why do you think she says these things? And is it possible that she’s saying this stuff while completely unaware of it?