I used to wake up screaming at the top of my voice or I would wake up feeling like there was someone holding me down and i could not move. I went to a sleep clinic and that helped. But there is a study that suggests sleep parasaly could be down to your mind being too active.
One of the things I did was get rid of all the gadgets from my Bedroom and I would meditate for a half hour before I would drop off. It certainly helped. I would askbthe G.P. to referee you to someone if it is bothering you.