@cstross For a while when I was a kid (ages ~11-18), my bedroom at my mum's place was a sleeping loft in the eaves that had room for just a double mattress about a foot of carpet and then an eight-foot drop. If I had rolled off sideways, I would have fallen about 4 ft before the middle of my body was stopped by the counter dividing the kitchen from the living room. Felt absolutely safe, no worries. Only once did I accidentally climb backwards off the edge to be found crouching half-asleep on the kitchen counter having broken the teapot.