Do you believe in ghosts?

OK, so I normally wouldn't write about this stuff, but I think we have a ghost in my house and just typing those words make me feel like a crazy person. As some of you know, I had my first 'home alone' night last night in a long time. Since we moved into the house, I have never felt totally alone if you know what I mean. I have seen what looks like a transparent person walking down my hallway towards our bedroom and disappear before. It's like a flash, so I always think that the shadows are playing tricks on me. Anyway, it happened again last night, but it looked as though it floated towards the kitchen. Then Zoe, my cat, started going nuts in the kitchen and meowing at something that didn't exist above her - I was in the kitchen with her and saw/felt nothing. I also saw (twice) a flash of light out our back door. If you've been to my house during the day, you konw that nobody lives behind us and there are no streets. It looked like it flashed on the deck. And, this is the strangest thing, about 5 minutes after Jeff and I laid down to go to bed and I heard a voice - like a whisper. It was a woman's voice and it sounded like it was in the hallway outside of our bedroom door. It's the voice that scares me the most! It didn't sound familiar and I can't remember what it said - it hapened fast and sounded like it started with an S - perhaps "shut". I knew what she said last night, but then I forgot while sleeping terrified. Jeff said he has heard things but assumes it is just the cats. One time, he got up in the middle of the night and because he heard what he though was glass breaking, but found nothing. I feel like a crazy person.