Accidental SP

I woke up in the night, and as I laid there, I began imagining myself running out of a building. After maybe around 10 seconds after I started imagining running, I felt a strange sensation move up my body, starting from my feet. Then, suddenly I heard what seemed like a high-pitched scream that quickly increased in volume until it was extremely loud. Unlike a scream, the pitch remained constant, and there were no further fluctuations in volume. It was extremely unpleasant to listen to. I kind of roused myself a bit by accident, and then it happened again. As I was unprepared mentally on what I was supposed to do, I never got into a lucid dream, but it was a pretty weird experience.