How to sleep for 4 hours without any problems

(1)Napoleon’s way of sleeping >
(2)Is Kim Ssanggyu’s sleep different
(3)Professor Shin Chul, Department of Medicine, College of Medicine, Korea University. The first difference is that he doesn’t wake upOnce you fall asleep, you never wake up Waking up
(4)If you look here, when you sleep for the first time, there’s a 90-minute cycle without waking up
(5)In case of this person, you might think that you slept for 2 hours and 3 hours
(6)You can get high-efficiency sleep without REM sleep