I have never worked shifts, but it would be no problem to me at all - i can sleep literally anywhere at any time I wish, for any amount of time, long or short.
I can fall asleep in a busy park at midday on a summer's day and sleep soundly for hours, no problem.
I can always catnap in my car, for anything from five minutes to three hours.
When I was workng, and knackered from being out at gigs, I could catch fifteen minutes in a toilet cubicle, now that takes effort, but i can make myself sleep when I want to.
Try the circumstances next time you are in a public toilet cubicle. You can't lean because you will slide off the seat, so you have to sleep sitting upright on a seriously hard surface, with bright lights on, and people coming in and out and making 'noises' as well as flushing and washing hands.
I can do it, but I am just lucky to be made that way.