Bad thoughts, very bad

I have the greatest ideas sometimes. Sigh.
My mind is taking some of the Creepypasta stories I've been reading and other assorted thoughts and stuffing it all together - complete with music - into one giant thought pattern. "Hate My Way" could be playing, and I'll get horrible images from when I self-injured complete with monsters looming in the darkness, watching me and telling me that I needed to do that.
Last night I had a period of time in which I had thoughts of harming others, which is completely unlike me.
Right now, all I can hear is a repeat of the same lines from the song "Ellen West" by Throwing Muses in my head as I type this out and try to get my thoughts down.
"Courting Ellen West,
Dancing on her grave,
Saving Ellen West,
My house is full of demons, I swear to GOD..."
It doesn't feel like my thoughts are racing, they just feel fast and hard to grab on to. I don't hear chatter, it's more of an introvert-type thing. I get so deep in thought that anything I think will be long gone in a nanosecond.
Today at lunch my best friend told me that her mom had been being ****** again. Her mother called her worthless, stupid, pathetic, lazy, you name it. She even suggested that this friend's boyfriend didn't love her because how could anybody love her?
And I suddenly felt the greatest wave of rage that I have felt in a long time. I never get angry. But at that point in time, I could have slowly tortured her mother to death. My friend is none of those things which she said. I don't remember what I said, sadly, because I fell down into a spiral and couldn't stop going fast for a moment.
All I remember is calling her mother a worthless c**t. Which, I know, I shouldn't be saying at my age...but I don't know what happened, everything just shut off in my head.
My God, I went way off subject.
Sorry.
I'm actually going to go to bed and listen to music for a while.
Goodnight.

I find it very strange too the way such thoughts of violence, even when you're not a violent person at all, including thoughts of suicide, is such a 'normal' part of who we are. Does it happen to other people? I don't think so, may be. I had thoughts of smashing my dog's head against the wall if he attacks my cat again. How weird that we have these thoughts and then are able to shrug them off or live with it as if it is normal. I always wonder about where those thoughts find rest in my brain and if that special place for them will in any way play a role in who I am or become?