Often time, right as I'm JUST about to fall asleep, (and this must have happened at least 100 times by now,) I see myself in first person, I'm walking, and then suddenly I slip. The sensation of falling makes me jolt awake with butterflies o__o. The whole thing usually lasts about 5 seconds, tops. One minute I'm trying to sleep, the next minute all of a sudden I'm tripping. Could be slipping on ice, tripping on a crack in the sidewalk, and one time, I got a basketball thrown at my head that bolted me awake o____o

Does anyone else ever get this? Or do they know exactly why it happens?