What does it mean when you have a dream of somone comming to kill you?

I keep having dreams were someone I don't know is running towards me to kill me I never see faces. The first one was in a dark ally I know the place I walk though a lot for my lunch in the day when it's light I've never been there whilst it's dark I'm walking alone when a hooded person walks towards me and pulls out a knife stabs me once and runs away, it stops there I woke up screaming in the fetal poisson. The next on is I'm sat on a park bench with 4 friends that I know very well when a tall figure comes from out the bushes wearing a trench coat in my dream I grab a friend the figure then stabs all my friends and then stabs me last, I once again woke up screaming but garbing my pillow this time. These are really scary realist dreams and I need to sort them out, please help