It sounds like you might have something that I get from time to time. You randomly just get images in your head that are graphically violent and severely disturbing. I fucking hate them, because I feel like I have some psychotic killer buried in my psyche. The thing to remember is that the fact that you hate these thoughts means that you actually don't want to commit them. My friend was the first person outside of myself that I knew had this happen to them, and he calls them the "The O's," because it's the obsessive-only side of OCD, or something like that.
Even though there's really nothing to worry about, you should still get in touch with a professional and talk this over with them.
-------
See my life come undone: Watch it go and let the damage run.
And I'd change the song, now, if I could - In the slickness of your blood.