I have had episodes of sleep paralysis, and in doing research and talking to my dr. it appears that it occurs mostly due to lack of sleep. Which would make sense. Since reaching the REM stage of sleep is so hard for us and our quality and quantity of sleep is so poor.
It's hard to say what triggers it in each person. According to sleepeducation.com, Normally your brain causes your muscles to relax and be still as you sleep. This is called “atonia.” Sleep paralysis seems to be when this atonia occurs while you are awake. So it occurs at one of two times, when you are waking or falling into sleep and your body cannot make the transition into REM properly.
My episodes occur upon waking, they do occur frequently, I am paralyzed from my neck down in horrible pain, they have lasted up to 20 minutes. It was scary for me at first bcs I could not move, but then after it happening I now just wait it out, and the pain is what bothers me more.
Have you spoken to your DR? I also have Narcolepsy, and I did see that this condition is very common with other sleep disorders. I would absolutely talk to your doc to get a sleep study in. Hopefully this helps <3 ((hugs))

Just happened to me this morning. Couldn't even call out to my hubby. Could not talk. Very scarey! Just a new symptom to add to my list!!!

Do you have tuple breathing? To try to move your neck and you can't? The worst part for me is trying to scream for help on one occasion my parents have heard me try to scream with my mouth closed and were able to shake me out of it but I will wake up frightening gasping for air and just want to be able to move it's extremely terrifying and I usually end up crying from the Trumatic experience even though I've had them multiple times!

I suffer from episodes of sleep paralysis.. I hate it that's for sure. I don't know what triggers it in my but I do know at time I have it when I've had lack o sleep.