I suffer from it. It only happens when your sleeping on your back. It freaked me out the first time it happened when I was 12, now i'm use to it. No episodes lately
It's scary though, buzzing sounds in your ears, can't lift your head or move your body, can't yell
(even though in your mind it seems like you are yelling) and I notice a dark shadow over me. When I was younger, I thought aliens were abducting me LOL.
Try to move your fingers or arms, within seconds your body will get up.....