Oh you poor thing, that sounds incredibly frightening!

I would have had trouble sleeping after that too.
I did have a dream once kinda similar to the one you were just talking about. My neighbor is a social worker and she used to work in the mental health unit at a hospital. She had come over to my house after work and was telling me about a patient that she was currently seeing (for legal/ethical reasons she couldn't tell me his name) So she dubbed him "Ned". This guy had come in and was convinced he was posessed and after spending the day with him, she was almost convinced too! lol Anyways, he was 'possessed' by this guy with a really old school posh english accent and he would "come out" of Ned occasionally. During one of his assessments they were trying to come up with solutions as to how to treat what was going on. One of the nurses jokingly suggested an exorcism. Ned is sitting there and this person inside him goes "You won't get rid of me that way!" and then went back to normal and Ned starting talking about something else. Spooked the crap out of everyone!
So.. onto my dream. That night I am asleep and my mind is blank, all of a sudden this voice starts talking to me, and it was the person inside of Ned. He told me he didn't want to be with Ned anymore and that when I wake up, he will be inside my mind. I could feel myself in my dream becoming incredibly distressed, not wanting to wake up as I was starting to freak out about this guy taking over my mind and really struggling to stay asleep, I could feel myself starting to wake up and when I did wake up, I woke up screaming because I thought I had been possessed! It took me a good few minutes to calm myself down and realise I was perfectly fine and it was just a nightmare, but omg, that was an incredibly frightening dream! (and this is an incredibly long post lol)
So I am feeling you on creepy dreams! I hope you get a better nights sleep tonight! *hugs*