Take it from a pilot: the average healthy person has no trouble with a few seconds of 5g, even 7g. With a few minutes of training, you can sustain that for a while, long enough for a loop or roll. I'm no marathon runner and had no issues doing 6ish Gs during sustained acrobatics (cuban 8s etc). Fighter pilots have to sustain higher numbers (9g) and remain alert enough to continue fighting, a far higher requirement than being pax/cargo on a suborbital.

FYI, being "fit" doesn't necessarily help. People with higher blood pressure actually do a little better than those without.