Have you ever thought you saw, but when you checked nothing

I was sitting at my computer this evening and I will swear on a document that I saw someone pass by my bedroom door that was open 1/4 of the way. That feeling came over me, the one when I feel as though I am not quite sitting here in 2009. Then that someone passed by the door again, this time in the opposite direction. This time I got up to look and of course there was no one. The person was wearing a pastel yellow top, that's what caught my eye. No, there is no one in this house other than my cat and I. It is or was likely not a solid human being. I have had similar experiences in the past and one time I got scratched by a cat that wasn't there too. I still have the scars on my hand. I was sitting by a fire in a house I lived with others. Someone was playing the guitar and there was a door that I was near and suddenly my hand was bleeding, two lines and I glimpsed a cat who wasn't solid. It made no noise and it disappeared when I looked straight at it. When I exclaimed I just got scratched they asked me if was our cat and said no, it was a ghost cat, a cat that wasn't there. Same feeling that I had with the person in yellow. I'm wondering if it is not the area or the situation if it is me, if I am haunted?