Why do I have Violent dreams?

[YepaItsmeeee]

Why do I have violent or weird/morbid/sad/nightmarish dreams most of the time? Like today, I had a dream that I was at a circus or something, it was really scary,there was music and everything, at first it was cool but the deeper I got the creeper it was, and at the end of the hall was a polka doted curten which I refused to go in, there was a horrible feeling, then I flashed back to this other place. with my mom me and a few other people, then I was walking home and I got lost so this guy took me in his car and I went to his house and we were watching a movie or something, and all of a sudden there were these guys who were being killed and tortured and got there throats slit violently! It flashed back to the same guy calling his friend crying how horrible that was. Then I forgot what happened, then the other day before I had a dream about a girl coming out of this white portal thing saying that God will punish the Earth or something, and zombies started to take over, right? So I remember going through all these places trying to survive, at first I was on my own, then I got to this school type thing, where we were killing zombies and stuff, my friends got infected and they were lying to me to make me let them in, but I didn't. alote of things happened I just don't remember, it was practically a movie, I just don't remember. After, I got home to my house and my mom was there, my grandma, my aunt, my other aunt and my two little cousins, by now it had gotten worse, the wind was blowing hard, the sky was grey and there was this black hole slowly forming in the ground, and the same lady who came form the white portal came out from this pod that appeared in the ground, with her husband and little kid, she told us that the black hole would consume everything and was put here by God and that it would destroy everything, but she offered to take me and my two little cousins, because that's all that would fit, I was really sad because I would leave my family, mostly my mom, she has given up alote for me, you know? so I carved 'I love my mom' inside the pod so I would remember her and that's where it ended, I started crying when I woke up. I have had a tone more weird ones but I got tired, can anyone explain WHY I have so many nightmares? and never a happy dream? My mom told me, ever since I was a baby, I would wake up crying, and during my toddler years I would wake up screaming in the middle of the night, for no reason! Oh and I would like to know why I always look like a diffrent person than I am in my dreams? Thank you!