I had a co-worker who could sleep with his eyes wide open. It was incredible. He would sit totally upright and put his hands, folded, over his belly. He would then sit at his terminal and just stare. I would walk up and ask a question, get no answer and finally figured out he was sound asleep. He started to snore. Loudly.
I got a group of people to stand around him one afternoon and we watched him for about 8 minutes. He finally snorted really loud, stretched, shook his head and came to. He looked at us staring at him and confessed. He learned how in grad school. Said it was so boring he had to sleep.
I didn't think it was possible until I witnessed it. It was beautiful. If I could, I would.