What does this mean? what is the problem?

iam good, sweet and kind but....when i feel lonely, get hurt emotionally or ignored badly then i become evil like a different dark personality takes over me.....i become senseless and careless about the world and i lose all pity for ppl and i feel like i wanna hurt ppl on purpose and i wish that all couples break up whenever i see any couples and i start to do bad stuff like for example entering a door and leaving it to hit the person behind me without holding the door for the person and like that and i just feel like i wanna hurt someone but......when i calm down then....i return back to my sweet and good self again.....it's somethin similar to 'the strange case of dr. jekyll and mr. hyde' but the difference is that i know and remember what iam doing and it's not a split personality disorder hehehe so......what could be my problem?