Re-occuring dream of a bloody classroom

For a year now, I've been having re-occuring dreams- creepy ones, that always make me wake up with chills. There are tons of them, going from kinda odd to just plain terrifying. Most come once or twice and then go away, but one just keeps comeing back and it scares the hell out of me. One that makes me wake up in a cold sweat,shaking hard.
I'm in a classroom, an unfamiliar one, full of people I don't know. Everyone is cold and empty, staring at the front of the room, looking at a chalkboard with odd writing that I can't understand. My best friend, Hannah, is sitting beside me, and she's the only one in the room that seems normal. It's like I'm both watching my body and inside my body, if that makes sense.
We sit there like that for what seems like an eternity, but it was probably only a couple minuets. No one in the room talks, or moves- it bareley seems like they're breathing (including me). We're all like statues- except for Hannah. Then, I feel something running down my right leg. I reach down to whipe it off. My meet something thick, like molassas, and sticky. When I pull my hand up my fingers are covered with black/red blood. My leg is covered in deep gashes, exposing the bone. Now of course, Hannah is freaking out,silently screaming for help. I tell her to be quiet, like this stuff happened to me a lot, and I turn back to the front. I looked at the blood on my fingers, and slowly put my index into my mouth. And I have to admit, in this dream, the blood is like nothing I have ever tasted. Hannah screams and a faceless teacher walks up and tells her to be quiet. I'm still licking the blood off my fingers.
The teacher says she'll bring me a bandaid, and leaves. Hannah is so speachless she just shakes her head and looks in front of her, her mouth open. The teacher came back, gave me the bandaid and left. I put it on the desk in from of me, and stare at the front again. Some time later the same thing starts on my left arm, only this time I SEE the gashes just apearing in my flesh. Now Hannah REALLY freaks out- she starts screamimg bloody murder. The teacher is back, this time asking her to silence herself. She says that she won't, not until I'm helped, and the teacher looked at her in a glassy stare. She suddenly goes quiet and looks forward like everybody else in the room. I lick the blood from my wounds and do the same. The teacher walks away and dissapears. Hannah is just like everyone else in the room; cold, empty, motionless. And it's the worst part; her just being forced into Submision. Her and I are like sisters, and we're both protective of each other. So when I see her being broken, it hurts.
I wake up then, and I can't stop shaking, and crying because I couldn't protect her. It happens about once every two weeks and I never get used to it. Dreams always mean something, but I can't figure out what this one means. If anybody has a theory, please tell.
What does this dream mean?