stomach, back, side, usually in the hangmans position (one ankle propped behind the knee of the other)-
I've been known to sleep upside down during times of insomnia or distress-draped off the back rest of a couch, under piles of clothes, in closets when I was younger; cupboards, shelves, behind dresser drawers, on top of things. (shhhhh bathtub). I also manage to sleep standing up if totally exausted.
Currently I sleep on a camp cot, restricting my movement (and keeping my room cleaner). But I keep the regular mattress in another room for those 'I need to sleep on a regular bed' nights. I sleep like I eat; it is really just a neccesary function-no whooplah involved. Almost always with the heater to capacity. I think I am simulating the womb. I can't STAND to be cold while sleeping. Not even a tiny bit.
I classify myself as a funky sleeper-er sleep freak. Sleep is awesome and can be taken anywhere 
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"I'm sorry Katya, my dear, but where we come from, your what's known as a pet; a not quite human novelty. It's why we brought you.... It's nothing to be ashamed of, my dear, but here you are and here you'll sit."