"Ladies of that era were much given to vapours, I believe."

Actually, the term "vapours" (never "vapors," because American women didn't have them, as such) was a euphemism for 'intestinal gas,' going back to England in the 1420s. It grew to mean, over the next two centuries, 'a morbid condition supposed to be caused by the presence of such exhalations; depression of spirits, hypochondria, hysteria, and other nervous disorders.'

[Source, Oxford English Dictionary, as quoted in "Forgotten English," a desk calendar I got for Christmas, under the word 'wamble', meaning 'to twist as in the wind.']

And 'the vapours' certainly could have been what drove the lady to the ground in a faint (feint?).

Bob