There are similarities between the atmosphere on Earth and the atmosphere in a pressurized area on a spacecraft, so breathing and surviving is not extremely difficult. However, there is always some feeling of weightlessness, so astronauts do have to take this into account.
If an astronaut would simply try to lie down on something soft, they might drift up, as would anything else that is not tied down. Because of this difference in gravity, an astronaut usually has to strap into a seat or attach sleeping equipment to a wall.
Space travelers have to take another element into consideration when they want to be comfortable and when they need to sleep. The spacecraft’s position in relation to the sun can be a problem. The sun may not only cause the area to be too light, but may also create uncomfortable warmth.
Space station cabins for individual astronauts are sound-proofed, so that helps. However, they still have to attach themselves to something to be able to remain in one place. To make their situation as comfortable as possible, and as close to their Earth habits, an astronaut may attach a sleeping bag to the floor or wall.
In space, it is just as easy to sleep in a “vertical” position as any other because the lack of gravity means the astronaut does not have to deal with up or down. When sleeping vertically, the individual must tether the arms and legs to keep them from floating as well. Being in contact with a wall helps the astronaut feel a bit more like they are in their regular sleeping space.
Still Not the Same
But sleep studies on astronauts in the space station and on space shuttles indicate that these individuals still suffer from sleep issues, in spite of all the preparations already mentioned. There is sleep deficiency, so some individuals have to use medications to help them sleep.
One of the problems has to do with the contact or lack of contact on the body, which was touched on earlier. Some astronauts have more difficulty with this than others. Temperature control is always an issue in space travel and living in space. One person might be too cold, while another might be too warm.
It is interesting to note the difference in “daylight” and “nighttime” as well. If a spacecraft is orbiting the planet, the light/dark cycle can be very short. This will have a significant effect on the circadian rhythm, or “body clock” of the individual. One method used to combat this issue is artificial lighting and light with short wavelengths.
To sum up the issue: It is possible to sleep comfortably in space, though this may not be as comfortable as it could be on Earth. Astronauts are in remarkable physical condition, so health issues are not the problem. They do get weary and they do need rest. Anything they can do to make their sleep time parallel the time at home will probably be tried.