If you literally translate this expression, you get “to fall in the apples”, which doesn’t make any sense. In fact, tomber dans les pommes means “to faint” or “to pass out”. This expression, that first appeared in 1889, doesn’t have a very clear origin. According to one theory, it comes from the verb pâmer (“faint”) transformed into paumer and then pommes. According to a second theory, it comes from Lettres à Mme M. Dupin form the French writer George Sand. In those letters, the writer uses the expression être dans les pommes cuites (to be in cooked apples) to refers to someone who is exhausted.
French with Valerie 