I fall asleep in any position on almost any surface. Growing up, I basically slept almost everywhere in my house.
Bathroom floor, the bathtub, ,the floor in my room, living room sofa, under the living room table, two chairs standing next to each other at the dinner table, under the dinner table, ON the dinner table (remember my parents got pretty angry with me that time), living room armchair (i was lying in it like a bed... somehow), living room sofa back rest I guess you call it? and under my bed...
Yeah, nothing really stood in the way of me sleeping when I was growing up.
Nowadays I usually sleep on top of my bedsheets in my clothes, actually in my bed like a normal person or sitting in my chair with my head resting on my desk. Oh, and I still sleep on the floor sometimes, I don't know why, but I just can't seem to shake that habit.