Could you be carrying guilt over something? Sometimes it indicates that you feel you deserve to be punished for something.
Yikes, that is no dream, that is a nightmare. Must be afraid of something in your life. May be you watch to many detective films. To start dreaming better dreams, sometimes it is good to play music as you are going to sleep. Volume turned down so it don't wake you of your favourite songs, pleasant songs, and soon your mind will be elsewhere and you won't have so many negative dreams. Relaxation excersice cd's and so on are great as well. Gets into the subconcious and helps change your way of thinking
It might be because you eat sweets before you go to bed. Try to think about something else or watch tv before you go to bed.
Maybe you have a problem with someone, if so see that person ASAP and sort it out, You may start to sleep well again with nice dreams.