Okay, So I'm pretty positive this is not normal because it is something I never did and never have heard of others doing..
One day, I walked into my little sisters room quietly without knocking.. and she was dancing around and doing all these weird motions, and seemed very out of it. The second she saw me watching her, she looked shocked and screamed at me to get out. Later, I went and asked her what she was doing. She told me ever since she was very young she has been doing this. It all started when she was still playing with dolls. She does this as a regular hobby. She will put on music, stand up, and she can make up a story in her head without even thinking about it. And it is like she is out of her body and into the characters. She tells me she thinks of amazing stories, and she can't really tell what she is doing when she thinks of them. But she just moves all around the room, and she thinks she is just acting out the characters motions but isn't really sure. She can create stories that are amazing, and they are word for word. She knows every word they say and just thinks of it as if she is watching a movie. She has no idea what it is, but she said it is fun and takes up a lot of time. She has such an imagination. She is eleven now, and still does it. Does anybody know what this is? I'm just curious to find out, I think it's really weird and interesting.

She's young... and using her imagination still.

I wouldn't worry about it at this age. If it continues into her early teens then it's an "issue".

She sounds very involved in her role playing. Lucky HER that she can bail out of her own life and go into a magical world.

Why is this a concern exactly?

Thank you.
It's not that it's a concern, really. It's just I'm curious about it, I think it's interesting. What would be the issue if it's into her early teens?

I don't see how this would be an issue when she is older. I put on music and bust a move all the time. Sometimes I act out lines from books I've read. Who cares? You're alone, using your imagination and just entertaining yourself. I don't think this makes someone a psycho, weird, or abnormal.

She's fine she just acting her age let her have fun we all did goofy things when we were little.

Maybe you can describe what she does in more detail..

I'd like to be more helpful, but I think I need you to give more details, like is music on when she is doing this? Does she do this w/out music?

This doesn't sound like something to be concerned about to me. Curious? Yes, very curious. But I actually think this is a very good thing. It sounds to me like your sister has a remarkable imagination, which is something a lot of us lose or never have to begin with. I am actually jealous-- I hope she has some sort of creative outlet to express this kind of energy-- perhaps dance, or acting/theater, or fictional writing?

If this was involuntary and uncontrollable, this would be a concern. She snapped right back to reality when you came into the room, and she says she does this consciously (preparing music and getting into position standing). She also screamed at you when you found her, so she's aware that this behavior might be seen as "abnormal" to other people (... god I hate that word.)

Conclusion-- she's just being creative. Eccentrically so... and who couldn't love that?