Deborah and I both roll on our sides to go to sleep. We roll on opposite sides, away from each other. During the course of the night, we each wind up on our backs, flail around a bit, get up to pee, talk to each other and roll back onto our respective sides to go back to sleep. That is, when insomnia has not reared its ugly on one or both of us.
In the morning the bedding is a mess. I can't quite track the physics of this, but the sheets go one way and the blankets go the other. My speculation is that I grab all of the bedding when I roll to the left and Deborah only grabs the blankets when she rolls back to the right, thereby leaving extra sheet on my side of the bed and extra blanket on her side.
The morning result is so consistent that it seems to be the work of some universal truth rather than nightly sleeping patterns. I would consider testing this theory with an experiment, but that would require sleeping on the other side of the bed. That will not happen. There is nothing more anxiety-producing and insomnia-inducing for me than sleeping on the right side of the bed.