I've experienced it at least twice, first time was really scary as i could only move very very slowly(slower than snails pace) and i heard high pitched laughter, also the tv was displaying some really freaky ****.
Second time was slightly more pleasant as it only lasted the best part of 4 minutes compared to 15 minutes of pure nightmare, all i heard was a buzzing sound in my right ear and some sort of shadow appearing out of my wardrobe, i managed to break out of it by constantly telling myself to wake up.