What is my problem?

I have this strange thing I can’ t explain. I was afraid of the dark when I was little but not anymore. I can stay in completely dark rooms without being afraid. Now I have a problem that I always look around me when I go to sleep. I am in my bed and every fifteen seconds or so I look around me as if I expected to see some strange creature . My room is not completely dark because there is light from the computer. This happens also when I take a nap during the day. Am I paranoid? Does anyone else have this issue? I am 16 by the way.