i feel like killing my sister?!

Anger management classes, or even just plain old therapy. There's nothing wrong with going to therapy, people make such a big deal out of it and a lot of people actually benefit from it. But, I think you should "nip this problem in the bud" so to speak, because you don't want to actually end up hurting anyone (or yourself) for that matter. My dad has anger issues and he never got counseling for them. He should have though, because now he has a lot of problems at the moment because of his extreme anger. Don't let it get to that.
Take care! <3

You need anger management - what you just said is pretty worrying!
I don't think you are mental or anything, at least you realize that you CAN'T follow your impulse and have self control over this. But seriously, anger management would benefit you a lot! x

See a counsellor.

Do it, it will solve all your problems, dumby.

two words:
mental hospital
NOW