Another thought on this occurred to me. Most people, when they go to sleep, are essentially paralyzed because the part of the brain that controls movement shuts down. But there are a few of us (yes, I'm one of them) who move around while they sleep. I had long suspected as much about myself, but it was confirmed when I had to do a sleep study to see if I had sleep apnea. Apparently, I move around even when I am deeply asleep. I don't get up out of bed (though I've fallen out a time or two
), but I toss and turn, often all night.
Combine that with the stories we've all heard (and some of us have seen) with things getting caught in the trigger guard, causing a gun to fire, and see what you come up with. A pillow on top of a pistol or revolver, the pillowcase gets into the trigger guard, the sleeper rolls over and his arm goes under the pillow (without him being aware of it), the handgun moves in just the wrong way, and
BLAM!