Do I have anger problem or a alternate personality?

I kinda think I have both but I am still not sure. I am the type of person who you would least expect like that one loner kid in class who never talks or you never notice he or she existed until someone points him or her out to you, yeah Im one of those who are a mystery to others, haha I still am until someone gets around to talk to me then everyone knows me.

Anyway, more to the point. I am not someone who is easily mad. You can bump into me or step on my shoe and I wouldn't care, it takes more then that to get me mad. One time I was in shop class/wood shop what ever you want to call it and it is run my a female teacher who knows what to do and I am in a class who is filled with guys only and she is the only female in the room (I feel bad for her and wish the only girl in the class wouldn't skip out a lot). They harass her and b---h her out for being the only female and say stuff like "A woman cant run a class like this go make me something". One time one of them was barking at her that made my eye twitch like crazy I was 2 seconds away from throwing a chair or desk at him and maybe beat him to death (I was that angry) but wasn't able to because I stop myself from doing so. I punch the wall when I get angry most of the time or scream into a pillow till I pass out.

Sometimes I think there is more then 1 person in my head like a murderous type. I was told that I put my hands around my cousin's neck when I was 12 or 11 choking him but I didn't remember any of it, I even still dont remember it. When I look at myself in the eye in the mirror I can see someone else that isn't me, more like someone with blood stains and a psychotic smile laughing (it for some reason makes me laugh with it, I dont know why). Im kinda scared of losing my mind to what ever is inside my head that is making me laugh at deaths at anything possible like gory anime, movies, etc. and I dont know if its really me laughing which is what really scares me.

If Im able to stop myself from my anger I should be able to stop myself if "it" makes me want to kill someone right? I dont really know what to do about this or know what it is.

EDIT:
Im not a bad person, I am someone who is nice to others (sometimes too nice). I kinda think people are scared of me when I tell them things like this :(

 

First lay off all the gore, I ain't gonna get into that whole does violent media create a violent person arguement. I'm just saying If you really react that strongly to the stuff, then stay away from it.

Second, anger isn't something to be scared of. Its an emotion, and like all emotions it can be a genuinely helpful thing as long as you don't let it control you. If you're feeling angry than express it in a way thats appropriate to that time, place, and situation. For example the nest time one of those ****s starts something in your shop class, just say calmly but firmly state that they're starting to piss you off/ make you angry. If you're not the type for direct confrontation then channel that rage into a constructive hobby like art or cooking. You seem like the the type who already knows that violence is rarely the answer to a problem so I'll skip that.

Third, everbody gets angry some people just have better ways of expressing/controlling that anger than others. You seem to have a pretty good handle on your emotions in that you didn't attack a bunch of *******s in a situation that would have aggravated anyone. So you're probably worrying about nothing, if you do think this is a serious problem then see your school counselor. That's what he or she's there for.