Why do I keep having scary dreams?

Well I keep having horrible dreams, sometimes they're really creepy and scary. And now, I'm scared to sleep at night and I get quite jumpy at night. The dream I had last night was about a hooded man in a dark cloak thing and he was trying to kill me...And I kept changing locations. One time I was at a shopping place, then Whitby, the park and then my home. And it was only me that could see him. Really strange, I was so freaked out. And sometimes I will think that there is someone or something in my room. So now, I have to sleep with my bedroom door slightly open...Which is really embarrasing because I'm 18 years old > . < Can someone help me, give me suggestions on how to stop this. Thanks ^^