Whats wrong with me? (Can't feel sad?)?

I think there is something wrong with me, its been like this since I was a little kid. Whenever I would watch a movie and someone would die in it, I would either not really care or think it was totally hilarious. Then when I was six I learned that my grandma was sick with skin cancer. When my mom told me to make a card I remember thinking, "I don't care if she dies because she isn't even my favorite grandma." Then when she did die I didn't cry or anything, and I used to see her every week or so. Ever since then I've hardly ever cried because someone died, real or in fiction; I've either been unphased, thought it was really funny, or been fascinated by it. I always have dreams about me torturting other people to death etc. and I always think about death and torture before I fall asleep and sometimes when I'm daydreaming. I try not to and I feel bad really about about this, I don't want to be this way but it's just like death doesn't affect me at all! I just found some really morbid stories I wrote when I was 8 that were meant to be comedies, people's limbs were being ripped off and their faces ripped off etc. and I thought they were funny. I think something is really wrong with me, what can I do??