Bit of everything for me.
Start off on my stomach with right arm under pillow & left leg bent at the knee.
After just a few minutes I turn & place my right arm again under pillow with my right knee bent.
I’m fast asleep in that position but am vaguely aware of being on my back with both arms across my chest.
I used to be a side sleeper…that is until I bought a new mattress & rolled off the bed twice. Since then, I’ve forced myself to become a back sleeper…less chance of rolling off the bed!!!
I fall asleep on my side.
Once I’m actually asleep, I apparently turn into a contortionist unconsciously because each and everyday I wake up with a sore limb. Mainly a sore neck.