In May 2002, I was in college and was having a dream about a ghost chasing me, trying to harm me. Right before it caught me, I woke up. I remember breathing heavily and looking at the clock and thinking that it was way too early to be awake on a Saturday, when I felt something sit on the edge of my bed.
Whatever it was leaned over me and put its hands on my chest and whispered, "Good morning, Missy" in a dark voice as it pushed its hands to my throat and proceeded to choke me.
I couldn't move, I couldn't breath, and I knew that I could hold my breath for two minutes, but longer than that I would be suffocated. I tried yelling for help, but I could barely call out. My roommate called from the other room: "You're just having a nightmare. Go back to sleep."
All this time I was watching the clock, and as it reached two minutes, whatever it was disappeared. I jumped out of bed and ran to my roommate's room to yell at her for not helping me... but she wasn't there. I looked for her and she was in the opposite side of the house reading a book. She said she never heard me or said anything.
I was studying psychology at the time and I told the story to the professor. She said that it was very interesting and she thinks that what happens is that your brain disconnects with you motor nerves while you're sleeping, so I must have been continuing my dream as I was awake, but I couldn't move because my motor nerves hadn't reconnected with my brain.
It has never happened before, but she said it is very rare, but happens to people who sleep walk or talk in their sleep. But is dangerous because I could have suffocated!