But, as advanced and impressive as the ISS is, the sleeping arrangements are essentially a sleeping bag tied to a wall, inside a small fabric sleeping pod. Worse, in microgravity, exhaled carbon dioxide can form a potentially dangerous bubble around the astronaut/cosmonaut’s head, requiring them to sleep next to an air vent.

It’s actually not as bad as it sounds.

“You might think it’s uncomfortable not having a mattress or a pillow, but without gravity of course, you don’t need anything to hold you up,” Canadian astronaut Chris Hadfield explained in a 2013 video. “You can just completely relax and you don’t even need a pillow. It’s space, you don’t even have to hold your head up.”

Astronauts are assigned 8.5 hours of sleeping time, though studies of their sleeping patterns have revealed they generally get around 6 hours and often suffer from sleep deprivation. But while they’re asleep, do they dream? 

Sunita “Suni” Williams, one of the two astronauts currently staying on the International Space Station a little longer than they expected, was recently asked whether she dreamt of being in space whilst in space, or of being back home on Earth.

“That’s a great question, actually. My father was a neuroscientist and asked me that same question when I returned home the first time. And I didn’t really think too much about it when I was up here. But I do dream that I’m up here at times when I’m here. And I do dream that I’m home as well,” she told CNN.

“I think it, you know, it must be based on your experience and what you’re sort of familiar with. So a little of both. And what’s I think sort of cool is I took note of all of this. And after I got home last time, I actually dreamed that I was in space a couple of times.”

Asked about space dreams in a Reddit Ask Me Anything, astronaut Scott Kelly said similar, writing: “My dreams are sometimes space dreams and sometimes Earth dreams. And they are crazy.”

A few other astronauts and cosmonauts have been asked this question, describing similar experiences of at first mainly dreaming about Earth-based activities, then more space, before the space dreams drop off after their return to Earth.

While few have been drawn in on the specific content of their dreams, or else forgot them, French astronaut Jean-François Clervoy gave a little insight into how his dreams were shaped by his environment.

“On my first flight, I was in a sleeping box. It’s like a [sarcophagus],” he said. “But when you close your eyes and you float in weightlessness inside the box you can easily imagine that you are in a huge bedroom. And I dreamt [a] few times in space that I was floating in space. Not in a space vehicle but just in [a] vacuum. Just floating, no need to breathe or to eat.”

“It was very nice,” he added.