It is amazing that so little is known about sleep, I have studied and I have discovered several important things about sleep, one of which is that nighttime digestion improves, in many cases, tilting the bed, the head is a little higher that the feet, in other times also the orientation of the bed influence the quality of sleep, I find it interesting that NASA do these studies because I assumed that the pressure caused by the force of gravity directly affects the quality of rest, then the astronauts should sleep much better than us on earth, but I also discovered the essential point to improve sleep, postures, as I will explain in my future post. Thanks for the info.