It is related to sleep paralysis, I get SP all the time so I know a thing or 2 about it. Opioids make it happen much more frequently with me. Thats what I mean, opioids depress the respiratory system so combining that with sleep paralysis may be dangerous. You're right though, breathing during SP is the same as it is when you're asleep so going into SP on opioids shouldn't be any more dangerous than going to sleep on them.