falling asleep depends on why i'm sleeping. if i'm going to sleep for a full night's slumber i do so on my right. if i'm napping, i do so on my back.
if i'm napping i wake up on my back. i don't roll over when napping. if i'm doing a full night i wake up on my back or right side. i may then make a conscious decision to roll to the left and get 30 minutes more. but i can't do any kind of deep meaningful sleep on my left.