Paralyzed while waking up?

I've noticed that, several times a month, for the last year or so, I keep waking up at normal times, but unable to move or breath. Sometimes I can even hear when people come into the room, but I can't speak to them. I've waken up before with blue skin from oxygen deprivation. I heard it's called Old Hag Syndrome, but I nobody has said if it's dangerous. Can it be dangerous, and can it be responsible for deaths once thought to be spontaneous?