do astronauts sleep on their back
What is it like to sleep in space? The catch is that they need to tether themselves to something to avoid floating away in the air currents. Most astronauts choose to sleep as closely to how they would on Earth, in sleeping bags tethered to the floor, the walls, or the ceiling. In the microgravity environment there is no such thing as up, which means it's just as easy to sleep vertically as you would horizontally back home. It's also important to secure your arms (and legs) to avoid them hovering as you sleep.