Nightmares help!!!!!!!!!?

Last nights nightmare was very vivid and disturbing. To sum it up, a lady had a shotgun pointing at my head so I closed a door in front of me. Then I grabbed my daughter and put her in a safe place while my mom and i looked for the woman, using scissors as our weapons. She was nowhere to be found so we were leaving then she came out of an attic by the front door. I yelled for my mom to hurry and put the baby in th car and get it started. The woman dropped the gun so I went up to her and repeatedly stabbed her with scissors in the chest, face and head. She fell down and as we were pulling away she got back up and tried chasing us so I threw the scissors at her. Then we got away. Why do I have dreams like this, they are always gory and I know I'm sleeping and try to wake myself up but I can't!