this thread caught my eye since i had experience of this too
when i was a young teenager (13-16) i used to experience this too, i was always quite scared and did not like the experiences one bit
of what i can remember now it usually happened when i came home from school and fell asleep on the sofa watching ST: next generation and woke up not being able to move but being consious of where i was
i tried to break it many times, i thought if only i could start to wiggle my toes and move me legs etc it would end, but this did not always work
i was under a lot of stress, having trouble daily at school and had early mornings working as a paper boy so my exhaustion could be explained in a way
but i have not suffered from this is a long time, but life has been a lot better since then!
just my 2 cents worth
love rich