[virtualwhys]

Have had this experience periodically for most of my life, although more so during my teens and twenties (41 now, happens maybe 10 times per year).

Imagine waking up and not being able to move anything but the tip of your left pinky; furthermore, you're not in your bed but in some kind of nether twilight limbo that has nothing to do with time as we know it in waking life.

So, that's the starting point, basically awake in a coffin. Rarely I've been able to relax into the experience and fall back asleep, but more often it's been the herculean struggle to migrate the movement of that pinky to the hand, to the forearm, upper arm, and finally, somehow, roll over on my side and wake up.

As to its origins, not sure. Perhaps it's preparation for the final sleep, who knows; if so, still work to be done here ;-)