Go Ask Alice (Columbia University's online Health Q & A) question and answer on Sleep Paralysis:
Click Hizzy
this is the first i've ever heard of it, and it's kind of interesting.
i read that first info link that RUgreek posted. there were pictures of witches and a karate alien on it, so i didn't take it too seriously.
and a link from there to U of Waterloo (heh, UofLoo) and read some of the abstracts, most by j.a. cheyne. those seem fairly
boring, yet informative.
and Dr. Jorge Conesa theorizes that
populations that have lived in geologically active areas of the Pacific Ocean, the so-called "Ring of Fire", would report incidences of SP more frequently. i guess, suggesting a correlation between SP and geomagnetic effects, among other things.
ring of fire!