Is it normal that i have sadistic/abusive thoughts?

I have been experiencing a lot of thoughts lately that have to do with killing and torture. All I want to do is at any given moment just sneak up, hold someone hostage, torture them and then stab them in the neck. At times I feel like I really can't resist myself, so I lock myself in my room/closet or just stab myself in the arm with a pencil or something sharp.. I also started self-starvation because I feel like it gives me more "self-control" over myself and my actions, and makes me less likely to actually kill someone since I'm relishing in the fact that I am better than everyone else as I can starve; I have all the control now. I tried putting myself in the other person's shoes, but honestly, I wouldn't care if someone tried to or actually did kill me. Does anyone else feel like this, afraid of themselves, because they aren't sure what they're actually capable of doing? That they have thoughts of murder and are scared that they may carry them out? I also wish to BE the victim; to be in a sadistic relationship where I'm raped and/or tortured; I think about this a lot, ever since I was about 5 or 6, and have been suicidal since around 8 and 9. I don't really think I have serious issues, but I really want to know if I'm the only one out there that feels this way. I was also wondering -- if this ISN'T exactly "normal", do I need mental help??