Body is evolved to have fluid under pressure to resist gravity. You get rid of gravity and we aren’t built for it. I was peripherally involved in a research study where they were going to strap people to beds for three months with their heads below their torsos. Every so often they would be wheeled into a centrifuge to see if it would counter act the damage. It’s so risky you can’t do it in America so we had to use human subjects in Germany which was… on brand.