I would suspect that 'rapid onset' has caused problems in disorientation and physical limb/'head+neck' motion due to whatever movement caused the onset of the g rather than in any g related area. As MFS has said, even at 25g/second (gulp) it is 'over' in 1/3 second in your a/c in which time no part of the circulatory system will have responded. Movement towards negative g at a high rate would be particularly disorientating and uncomfortable.
A rapid onset of any g would cause significant disorientation and delay any remedial action. I would suspect that even 10g/second if unexpected would have confused me in my 'younger' days (said one who nows 'greys out' if he levels out from a descent while turning
). If in the positve direction, unless the head is restrained, neck injury would be likely. Certainly my ride on a Martin Baker (admittedly at a higher rate) slammed my head down painfully hard into my chest in the brief time the seat accelerated. I cannot recall the g rate on a rocket seat but I was eyes open and looking at the world (albeit through my size 10 boots) within no more than 1 second, in time to see (and react to) the seat separating during a low level ejection.
Regarding 'return' to normal g, it is certainly not in my book of favourite manoeuvres, but I cannot see any need to 'return' rapidly to +1 if the pilot is used
to -3?. For positive, it depends on the physique and protection systems - a rapid and unexpected onset will give no time for precautionary preparation such as pilots are trained to do, and therefore back to +1 g in a couple of seconds would enable a dazed pilot to recover over the next few seconds. I don't think the body would react that quickly in shutting off the brain supply.