well, its a common thing to act out your dream as your waking up from it but the violence is definetly bad. a violent dream could be the only dream you act out as you awake. everybodys different but it seems like your cousin and your special friend were just at the wrong place at the wrong time. I dont know... I'd start with interpeting the dream and take care of the problem so you just dont have those kind of dreams.
I hold invisible telephones to my ear sometimes when I wake up but I just TALK to the person on the other line, not choke 'em.