The human body is considerably more able to survive g-forces that are perpendicular to the spine. This is not true in 0 g when you strafe up; that is an eyeballs-down maneuver, which is the same force as a blackout where blood rushes to the feet, and this force is parallel to the spine. In general, when the g-force pushes the body forwards (colloquially known as 'eyeballs in') a much higher tolerance is shown than when g-force is pushing the body backwards ('eyeballs out') since blood vessels in the retina appear more sensitive to that direction.