ESA - Sleeping in head-down position In the absence of gravity (microgravity), the venous return to the heart is facilitated and the fluids in the body's interstitial tissue tend to redistribute upwards, increasing relative hydrostatic pressures in areas not used to such pressures, thus allowing the formation of fluid accumulation and oedema in upper sections of the body which are readily visible in areas with soft tissues. Examples of this are the astronauts' puffy faces and skinny calves that are observed in space. However, a similar mechanism also causes the puffy faces all of us see in the mirror when we get up in the morning after lying down overnight. It has been shown in bed-rest studies that head-down tilt -7 degrees reproduces to a fair extent the fluid redistribution observed in microgravity, thus it has been hypothesized that by having the cosmonaut sleep in head-down tilt prior to launch, will pre-condition the upper-body tissues to microgravity-like hydrostatic gradients and ideally reduce the stress on those body districts upon actual microgravity entry on the first days of flight and facilitate the overall adaptation to the new microgravity induced circulatory gra