For one thing, sleeping is more troublesome than you’d think, considering the remote location:

The onslaught of apparent days and nights would play havoc with astronauts’ body clocks, so a shutters-down and bedtime schedule is imposed by mission controllers. Each of the crew has a closet-like cabin where they can hook a sleeping bag to the wall and settle down for the night. Some strap pillows to their heads to make it feel more like lying down. The lights don’t go out completely, though. People dozing in orbit see streaks and bursts of bright colour caused by high-energy cosmic rays painlessly slamming into their retinas. Fans and air filters add to the distractions, so some astronauts wear ear plugs to block out the constant hum.

Unsurprisingly, falling asleep can take some getting used to. Just as you are nodding off, you can feel as though you’ve fallen off a 10-storey building. People who look half asleep will suddenly throw their heads back with a start and fling out their arms. It gets easier with time. One Russian crew member is renowned for doing without a sleeping bag and falling asleep wherever he ends the day. Anyone still awake after bedtime would see his snoozing form drift by, slowly bouncing off the walls, his course set by the air currents that gently pushed and pulled him.