Dream of

I have a recurring nightmare which is almost always the same. I am being grabbed in my bed from behind and can feel the persons warm body but cannot see them. I know it is a man and I fight and try to shout to get help to get him away from me. At fist I thought it was really happening but began to realise I was asleep and try to wake myself up. This has happened for a year now since I moved into my new flat. Sometimes their are two people grabbing me and I swear and fight them trying to see who they are but I never can! It always is in my room in my bed every time the dream occurs.