rules of flying
#3 recover physically from negative g's (flying upside down) before initiating positive g's (flying rightside up). specifically refers to split-s and cuban 8. during negative g's gravity pulls too much blood into your head. so your neck shuts down the flow to a trickle. when you immediately go to +3 g's gravity stops forcing blood into your head. your neck arteries open up again but that takes several seconds longer than it takes for you to pass out.