Something Passing Through?

I've always believed in ghosts. I've been a fan of learning about them and I find them so interesting. I'd never seen one. I have very high senses on certain things and major deja vu which I believe sometimes could let me pick up things other can't. My mother is also this way! I've lived in my home for years and it's in no way haunted from what I can tell. What I saw though, is something that I'll always, always remember.

I got home from shopping and ran upstairs to grab something. Note that the upstairs was fairly bright. I started to hear a shuffling or like someone is sorting papers in my room. I went in and stopped short. There was a black figure standing at my desk and it turned to look back at me. I ran into my bathroom on the side and when I could breathe I ran downstairs and told my parents, "I think I saw someone upstairs!" In the world today, my parents thought is was a burglary. My dad checked everywhere. Even checked downstairs and there was no one to be found.

I really did see a black figure and the noise it was making was very clear not to be coming from anywhere except my room. For more detail, it was faceless and jet black and when it turned around to look at me, I felt kind of sick to my stomach all of a sudden. For further detail on the sound, it was pretty loud and in my face now that I think about it!

The question I have to ask is: If my house isn't haunted, is it possible that a spirit could have just been passing through? Just there for a little bit and then gone? I know it sounds silly but I've had no further experiences. I'm just curious. Not even scared! I know I have nothing on some other crazy stuff other people have seen, but just please give me your opinion. Thanks for your help, little ghosties.