Thread: Challenged To A Duel (by Myself!)

First off, I have never been confronted by myself in a dream, in fact, I don't think I've ever had a dream where I saw myself in one other than in a mirror.

*dream*
I was sitting at my computer in my bedroom and my sister was hanging out with me. She opens my bedroom door, (which is just next to my computer desk), turns to me, and says: "It's you."
Surprisingly I stay calm through all of this. I ask her to please open the door again and ask if it's still there. (made poor sis into a guinea pig ) She does as I asks and tells me yes it is. Then, we both hear it speak (or my sister relays what it says to me; not sure).
"You can run or you can fight," it says. "Either way I'm going to kill you." Somehow, I still managed to remain calm. "Well, of course I'm going to fight," I say. My sister lets the other "me" in. It didn't look like me at all. I think she had red eyes and maybe stringy long hair. Demon-like. I can't remember the fight at all, only that we did, and when it was all over, I had won, although I was left with a bleeding, deformed right hand where part of my ring (or pointer?) finger was missing. I spent the rest of the dream thinking what had occurred was real, and I had the hand to prove it: I'd survived a duel with myself and won.

Later, I woke up, shocked that it had only been a dream. I checked my hands and they were both intact. But I was sincerely creeped out, and couldn't go back to sleep until I had watched a little TV to help me forget. I was afraid she'd come back. :/
I have a few theories on what this could be about, but I'd like to get some other opinions.