ESA astronaut Frank de Winne (right) with his team during the Odissea mission

You have to keep your feet anchored in loops on the "floor", of course, or else you would simply drift away. Sleeping is a matter of fixing a sleeping bag some-where and climbing into it, and as it can be quite noisy on board, many astronauts wear ear muffs."

The noise comes mainly from the ventilator fans which are essential to keep the air circulating at all times. On Earth, convection currents keep air moving constantly. But convection currents do not work in weightless conditions where nothing is heavier or lighter than anything else. Without the fans, the carbon dioxide breathed out by a sleeping astronaut would not circulate. The gas would remain in a bubble around his or her head.

Umberto Guidoni entering the Zarya module of the ISS.

Guidoni adds:
"The ventilation system also catches most lost objects, which sooner or later drift towards one of the ventilation grills. That’s what happened to my lost diskette, by the way."