I recently experienced extreme rage on MXE, but I went into it voluntarily and directed it at a virtual target (Having felt it, I sympathize with you as I imagine if it was involuntary the momentum of it would be frightening).
My girlfriend was gone for a few days so I dosed MXE and popped in "Texas Chainsaw Massacre," just because I felt a Halloween sorta mood. But as the carnage approached I could feel a demented joy welling up, like a calling from the sub-conscious. I was alone in the house, so I decided I would use the coming scenes to explore my dark side (to as extreme a reach as possible without externally acting on what I felt). It's my personal philosophy that the best way to control negative emotions is to start from a place of stability, then use media in conjunction with psychedelics to evoke the feelings in contained but still very powerful ways. It's my hope that in this way it's possible to learn to navigate the emotions during a time and in an environment that doesn't risk dire consequences -- to understand, intellectualize, and, ultimately, better control them if they should take me by surprise "in real life." I don't know of any other realistic way to learn to manage emotions so powerful preemptively, and would feel irresponsible if I didn't try.
The rage built and built, and I embraced it and pushed on at every new plateau. I peaked at a level of manic sadism, a bug-eyed, shuddering, gnashing, and drooling (all literally) lust for the death on screen. I was sucking in short, toothy, breaths like I was trying to cannibalize the moments. It was fascinating to find the MXE mania could express itself in a way so contrary to the peacefully innocent orgy of bliss that my best MXE experiences consist of. It was an orgasm of terror and hate, and I was searching and learning it. I was feeling the ecstatic rage of a psychopath in me -- presumably the one somewhere in all of us (certainly in most males, or else how can we explain homicidal-rapist soldiers or the sadistic prison guards in the Stanford Prison Experiment who were perfectly normal undergrads just days before? We're all that one special condition away from being a monster, but maybe we can find it within us first, and thereby hope to tame it.)
Then, at the end of the film, it just went away. I started laughing in amazement. It may have been the most satisfying laughter of my life. It wasn't a catharsis at having expressed such rage, but joy in that it was possible to feel something so horrific and then snap back into contentment, joy in knowing that such a delirious, marauding hate really never was in control, in seeing and knowing how truly silly it all was.
That dark side can definitely come to the fore on MXE. I remember watching Football Factory (pretty wank film in all honesty) and I got a huge buzz off the violence. I think that's healthy though, and I would describe it as cathartic.