However, Hobson and Stickgold find, from personal experience, that a few nights of training can save dreams from oblivion. When we tried it ourselves, recall wasn't too good at first. But by the fourth or fifth night, we were flooded with memories of our dreams. We hope the same happens in space. If Hobson is right, astronauts and cosmonauts will dream much more than they do on Earth simply because there's more motion for them to cope with.
Weightlessness takes away up and down as references.
Take sleeping, for instance. Astronauts can't lie down to sleep. They can't put their head on a pillow unless they tie it to their cheek. They often sleep in a bag tied inside a compartment the size of a telephone booth. On early flights, astronauts worried that lack of air movement would cause them to suffocate on the carbon dioxide in their own exhalations.