So how do Astronauts sleep aboard the ISS sleep? In that orbiting facility.They sleep incredibly well, and that's not entirely a joke answer. Each astronaut has a personal area about the size of a phone booth. (Um, it just occurred to me that some of you might not know what size a phone booth is, so look it up!) It looks like this (female astronaut not included):
Anyway, this area is their bedroom, their private lounge, their everything, in terms of being away from everyone else. They can spend time on the computer here and receive and respond to private messages from home. They can do anything private that they want to, as there is a sliding door to close themselves off from the rest of the station. (It has its own air supply that blows fresh air in all night, in case you're worried.)
Here's a shot that shows more of the interior, taken with a fisheye lens, which shows that each astronaut has their own computer station (male astronaut not included):
Most importantly, they sleep here. No mattress, no pillows necessary. They use that light green sleeping bag on the right, which is strapped to the wall to prevent themselves from floating away and bumping into things while they sleep. But in zero-g, you don't need to lie down, you don't need a pillow, you literally just close your eyes and fall asleep. And best of all, since there are no pressure points from gravity pulling your hip or shoulder down into a mattress and cutting off your circulation, there is absolutely no tossing and turning while sleeping. You are motionless for 8 hours and sleep straight through, uninterrupted, blissful sleep.
Astronauts returning from space all say that the one thing they especially miss is sleeping in zero-g.
Another interesting thing is that when they close their eyes, they might notice that they've just gotten hit through the eyes by high-powered subatomic particles called cosmic rays that smack right into their retina. These cosmic rays are so powerful and so small that they travel right through the skin and everything. Down here on earth, the atmosphere normally protects us from these, but on ISS, there is much less protection. This causes them to see flashes of light in the darkness, even while sleeping. Unfortunately, this has led to a very high percentage of astronauts developing cataracts later in life.