I'm currently reading a book called State of Wonder by Ann Patchett and this is a quote from the book:
"She knew how to close her eyes for two minutes. It was a magic trick she had picked up in residency, falling asleep in the corner of the elevator then waking up on the right floor."
Interestingly, I've read this type of things before in books... someone saying as a resident, they trained themself to fall asleep instantly.
Patchett isn't actually a doctor, and I'm going to go out on a limb to say she's got it wrong. Residency has trained me to be a much lighter, worse sleeper. I can't imagine any other outcome to having a pager by your head at night.