What does it mean when you dream about killing a man in self defense?

So I had this dream, where I was at my house. A friends dad was there, he's not a big guy, but he's not small either, and he can be a scary individual. So someone rings the doorbell at my house, and my friends father answers it. I'm watching t.v. when the door is opened. My ex is at the door. He lets her in and she goes back to a room. Then other people walk up who seem intimidating. They walk in and seem to be friends with my friends dad. They talk at the door. A guy and a girl walk in. The girl walks back into a room. The guy see's me and begins getting hostile, my friends dad tries to intervene and is knocked out. At this point, the guy has a knife, he corners me into the kitchen, and trys to stab and i put my left arm in the way, he stabs into my arm. As this happens I put my knife underneath his ribcage in an upwards motion. The man collapses and bleeds to death in front of me before i'm woken up. What does this mean, this is the first time i've had a dream of this kind. I'm generally a pacifist, I avoid arguments, fights, and any other possibly explosive situations, so this is not in my nature. Can anyone clarify a bit?