It's called the figure 4 position and lots of us sleep in one variation or another of it.
I can *almost* get there in my Ridgerunner, but it requires me lifting the bent knee and setting it on the edge of the fabric. Doable, but not terribly comfortable long term as that hem starts to dig into the skin after a while. Remember the pain from underwear elastic too tight on your waist? Same thing.
I can get in a lazy figure 4 OK in it, but not as well as in my gathered-ends. Doesn't really help you, but....