When I fall asleep, I really fall asleep. It's like turning off a light switch, BAM! So I do not drive when I am tired for example.
My dad, grandad, and youngest son were/are all the same. How abrupt is it? Well, one day when youngest son was 3, he went to the bathroom before going to bed, and didn't come out. Mr. Ski went in to check on him, and came out laughing like crazy, and said, "You've got to see this!" Sure enough, youngest son was standing up with his pants around his ankles and his head leaning on the toilet seat cover, sound asleep. Literally, out like a light.
So: when I fell asleep, I keeled over on the sofa and landed on the Kindle. Which broke. Nowadays, I have a reading strategy that takes into account possible landing spots