"Fucking Shit. Brain, stop it. I don't want to keep seeing myself stab people, or start breaking everything, or punching that cinderblock wall, or stabbing myself, or cutting myself. I don't want to. Just STOP. WHY WON'T YOU STOP? YOU ARE ME! LISTEN TO ME!"
Literally what I just said to myself. Help.
Intrusive thoughts, mate. They can be absolutely godawful; for example, i've had images of me punching and stabbing people (like you have, i guess), images of me committing suicide in more than one way and "mere" images of me suddenly smashing a nearby smashable object. None of these are things that i want to do (well, smashing things can be fun, but they should be destined for smashing in that case), and suffice to say, the image of me punching my brother in the back of the head is not nice at all. The best thing to do about these thoughts is to just allow them to be there, since, as we all know, it's basically impossible to say "i don't want to think of zebras" without thinking of zebras. Once you stop trying to banish them, they'll eventually get boring and go away on their own.
I've previously had problems with these thoughts becoming increasingly compulsive to act out (although it never quite got there), so much so that i had those pre-emptive sensations of movement in my relevant limbs, but then i heard and read about how it's actually extremely common to have these thoughts, and that trying to force them away just makes it worse. It's okay to have them, don't worry. Hell, it'd be much more worrying if those images weren't distressing, so i guess that's a thing?