My father was career Navy, he acquired some interesting 'tricks'.
He could sleep standing up,leaning slightly back on something!
That side of the family can nap anytime, anywhere! I have seen it.
A rainstorm came up, like they can in the mountains.
We all found spots under rock outcroppings, to get out of the rain. (No lightning)
20 minutes later, my friends found me sleeping, standing up, wedge into the rock outcropping.
In the movie Sniper, Tom Berenger goes to sleep in a swamp or pool of water. I jokingly thought...amateur.
I think I could probably sleep almost anywhere.