How does your body know you’re at the edge of the bed and prevent you from falling off when you’re asleep? Is it a “skill” that gets better over time? When I was a kid and shared a bunk bed (I was on the top bunk) with my brother, I fell off twice (and fractured my skull once), but it’s never happened since then. Somewhat similarly, I once fainted, and have observed others faint, but in no instance did any of us crack our heads on the ground. This, I assume, is probably a function of instinctively thrusting your arm out to break your fall before you lose consciousness, or possibly just has to do with the manner in which you fall when fainting. Still, the not falling out of bed thing seems odd to me - what weird level of consciousness is operating there?
your body inhibits large movements during sleep to prevent injury. in children because of the stage of development they are different.
went a person faints they often do so limply so that limbs and trunk hit the ground first taking most of the impact. if the body stayed stiff you would see more head damage.
Your problem may well stem from what you took at Woodstock. 
Sorry, but I have fallen out of bed a number of times. I don’t think this is guaranteed to be true.
Somewhat related (although it only applies to the REM phase of sleep):
Interesting. Evolution, as always, be wacky.
I can assure you, first hand, that adults can and do faint and smack their heads on all sorts of things.
I fainted and fell face-first onto the floor a few years back. Broke my glasses right in half.
I’ve seen a guy faint and he smashed some teeth out. I don’t think I’ve ever fallen out of bed while I’ve been asleep.
Agreed - falling face first is the most common falling “posture” when fainting - I’ve seen it many times.
Most bunk beds have rails on the upper to keep you from falling out. Did your bed not have those?
That’s lucky. I fainted and managed to drive my glasses into my eyebrow line and cut it deeply enough to need stitches.
Nope. My mom nailed a board across the side after the second fall.
I saw a woman faint at a Navy change of command ceremony. 400 people all standing in the hot sun for an hour and she keels over face first. She hits the ground and her short-hair wig flies off. The wig rolls across the ground between two of the guys standing in the squad in front of us, one of whom (possibly thinking he was being attacked by a rabid animal of some sort) began screaming like a little girl. Pandemonium erupts while the rest of us are laughing our asses off at the guy who’s screaming. Meanwhile, the poor woman is still lying on the ground bleeding. Ah, memories.
Because I sleep on the floor.
I’m pretty aware when I’m sleeping and I don’t think that’s too uncommon. I can wake up at a set time if I convince myself hard enough before I go to sleep, I can stay in one position all night (if needed), avoid physical contact if I’m sharing the bed with someone I don’t want to cuddle with, or make sure I don’t steal the covers. I slept in a top bunk with no railings most of my life, and I’ve never fallen out of any bed.
When I was on parade as a young soldier I would often see people “thunder in” while at attention or at ease, especially veterans and cadets. They would often go straight forward, like a board, between the rank in front of them.
Yeah, I can’t do any of that.
Most of the time, I’m lucky if 10 alarms and a train will wake me.
I fell out of a bunk bed a few times as a kid. I never fell out of my own normal-height bed. The bunk beds I fell out of were a bit narrower than the normal twin that I was used to, so my theory was that I had ingrained memory of how much squirm room I should have, and that a little less threw me off.
I’ve nearly or completely fallen out of bed multiple times as an adult. Of course, I also talk in my sleep a whoooooooole lot. I figure my brain does not completely shut down the voluntary muscle movement while I’m asleep.
DO they forget to bend their knees? Because that’s the most common way I’ve seen that happen.