The word “dizzy” evolved from the Old English dysig, meaning “foolish, stupid,” from the Proto-Germanic dusijaz and perhaps from the PIE dheu-, “dust, vapor, smoke; to rise in a cloud,” suggesting “defective perception or wits.” Its swimmy-headed sense arose in the 14th century.
Some early English translations of the Bible refer to the foolish virgins in the book of Matthew as “dizzy” in the “stupid” sense in place of the word “foolish.”
“Dizzy” was also used in relation to the “dumb blonde” stereotype as late as the 19th century, which may have gained particular popularity in the 18th century due to the comedic play Les Curiosites de la Foire (Paris 1775), inspired by a famous French prostitute named Rosalie Duthé who had a reputation of being beautiful but stupid.
Useless Etymology 