I routinely had 8+h drives in the rear-facing seat of my family's circa 1970 Plymouth Satellite station wagon growing up. Completely unsafe, and very boring, but I don't recall barfing.
My sister and I would pass the time folding up a piece of paper and each of us got to draw part of a person without seeing what the other had drawn. Sort of like visual madlibs.
Both, plus absence of seat belts. Rear facing with no head support is a good way to snap your neck if you are wearing a belt, but because we weren’t, we’d probably be flying forward to the windshield.