Is it normal to have almost completely separate personalities?

So for a while now, I've almost always had two sides to me. I've always either been the kind of person who's kind/caring/loving/selfless to the point of putting others well-being/happiness/safety before my own and can literally feel the emotional pain of others and shares their pain and will do as much as I can to support them and make the feel better, or I've always been an extremely violent/hateful/bloodthirsty person that wouldn't enjoy anything more than absolute chaos and would love to be in fights/battles/wars/various other life-or-death situations and would never hesitate to end any sort of life. Both sides are fully aware of each other and share the same consciousness and memory. It's almost like there's a switch inside me that when flipped, I become the monster that harms without even thinking about it and would gain neither gain happiness nor enjoyment from death and destruction of others or anything else... but craves to cause it. I'm constantly fighting with myself to suppress and keep my violent side from gaining control because I have a strong feeling that if I ever snap and give into that side, it'll become the primary "personality" instead of the kind and caring side.

Is it even remotely normal to have this kind of clear cut difference in how I act? And I apologize if there isn't a whole lot of info there...