Had this since childhood although it now only occurs once a year or so. It is frightening as hell. My mother has it as well. That makes sense its related to anxiety as I've suffered from it since childhood as well.
My sleep paralysis is so severe its caused me to fight sleep until I'm completely exhausted. Four or five years ago I was prescribed a medication for anxiety to be taken an hour before I plan on going to sleep. Interestingly, this is around the same time my episodes of sleep paralysis went down dramatically.