meaning of nightmare dreams

This is not a dream, but possible a nightmare. I have no recollection of waking up. I 'dreamed' that a black shadow was standing next to my bed. It just was staring at me. I was only four or three at the time, so naturally, I should have screamed, but instead, I was stuck in a terrorized silence state. As I watched it from my bed, it slowly reached out for me. It's movement snapped me out of my trance, and I screamed for my parents. I heard running down the hallway, and my parents appeared in my doorway. I pointed at the shadow, but it was no longer there. It had disappeared instantaneously, with no evidence of it's existence.
Obviously, I haven't forgotten it. I haven't felt the same sheer terror that I had felt then. If it was just a nightmare, then it's harmless to me. But on the strange occasion that it wasn't (which I still believe), it must have been a ghost, or worse still, a demon who had come to claim my soul. (Sorry, I sounded seriously loopy right there!) But either way, I need to know which one it is so I can put my mind at rest.