Every so often I have a psychotic urge toward violence. I never follow up on it, but it goes something like this. I'm sitting across the table from someone, and in an idle moment I think, I wonder what it would feel like to pick up this (insert heavy blunt instrument here) and strike them in the temple with it as hard as I can. Would their skull collapse? Would it simply strike with a sickening thud, and would their eyes roll up into their head and would they collapse, or would they fall to the ground screaming and clutching their cranium, blood seeping out from between their fingers? This could be someone I love, or someone I don't know from adam -- the feeling is the same.
I was in a car with a friend once, driving South from San Francisco on Highway 1 and she said, "do you ever have the urge to just drive the car off the cliff?" There was slightly more to it than that, but I froze halfway between fear that she would and telling her yes, I have that thought all the time. What would it be like to give the wheel a nice twist to the right and make a big jump off the gentle berm at the road's edge, and sail into the great blue yonder for just a moment, taking leave of gravity due to the influence of a simple machine (the lever, in the form of a ramp) before arcing down to the cold, hard water below, all at 80 miles per?
These urges come on suddenly and leave as soon as they came, and behind them is a vague disquiet - "Did that thought come from inside my head? Am I entirely sane?" But my conclusion is that it's a crazy world, and everyone's a little insane. The kind of person you are depends on how you react to those urges. If they leave you unnerved, you're probably doing all right. If they make you feel peaceful and free, it's most likely time to seek professional help.