We're so used to the waking/sleeping transition happening smoothly that we don't recognize how many different parts of the brain have to be perfectly coordinated to pull it off.

I was surprised to see half a million YouTube results for "sleep paralysis" just now. I was looking for a documentary I saw a few months ago, which I couldn't find again. It implied that because so many people report similar imagery (red-eyed shadow people led by a shadow in a hat) during sleep paralysis, said images must be real. They were not taking into account all the external, cultural ways that we have of synchronizing our dream lives (like reading and commenting on half a million YouTube videos, for instance). @mada is writing a series on this kind of stuff.