Voices? Am I insane?

I know you might think about this as having to be in a mental asylum or something, which I probably should be, but oh well. I hear voices in my head. They argue, and it's only when I see blood, or when there's a flashback sort of like Deja Vu. My friend Damian and I, we recently got back in touch from 4th grade, and apparently he gets so annoyed to the point where he's in tears sometimes. (We're now in 8th) But I've tried to tell him, I pretty much black out when they start getting at me, and putting things in my head, I don't know what I'm doing, then I'll snap out of it about 20-30 minutes later, and not remember where I was at, what I did, what I said, nada. I have an extreme fear of killing myself or someone during these times, because sometimes when I snap out of it, I'll wake up, have a knife in my hand or something, and I'll have cuts or my legs, or I'll be cutting something else. I don't know exactly what makes me do this or why, but it happens. Is there anything that anyone might think I could do? Please? I really need help with this.