The human body runs a risk of going unconscious when subjected to G-force above 6G for more than a few seconds.
Though, skilled professionals like the astronauts, fighter pilots, can withstand up to 9G and more, due to training-built tolerance inside the centrifuges.
Astronauts can tolerate that blood flow thing on brain upto this level? Thats pretty impressive!
A goo post btw, green bro. :)