My hubs even studied, wrote papers, and has a patent on that. I'm an idiot tho.
Here was my thinking, because I did think of NASA studies (not enough obviously):
Anything in space is weightless. Without the force of gravity, being "upside down" is meaningless. And most all NASA acclimating-to-space studies are done inside a freefalling plane. Water tanks have sometime been used but only to get astronauts used to working in a space environment but it's not entirely equivalent to the freefall. It somewhat helps them to acclimate to working extra-vehicularly in space, as they have had to do in working on the ISS
Thought I'd run this ☝ past the resident physicist here, so he corrected me and reminded me of the intracranial studies. 
There are many reasons human are not adapted to space travel but one of the greatest problems is rooted in our intracranial pressure.
- NASA spouse
Re:
https://www.nasa.gov/content/it-s-all-in-your-head-nasa-investigates-techniques-for-measuring-intracranial-pressure-u
https://en.m.wikipedia.org/wiki/Visual_impairment_due_to_intracranial_pressure
https://www.ncbi.nlm.nih.gov/m/pubmed/26099128/
https://www.nasa.gov/mission_pages/station/research/experiments/1038.html
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