The SP as a sleep disorder is not exactly "a medical condition in which the REM Atonia is active for too long" because when it happens, you are not in REM sleep (it happens when REM sleep is over, or not yet there), we could rather call it a N-REM atonia.

But yes, it's like the REM atonia is not well synchronized with REM sleep.

what do ya mean by "thus resulting in frequent episodes?" ?