Director Dario Argento said he actually experienced Stendhal Syndrome as a child. While touring Athens with his parents, young Dario was climbing the steps of the Parthenon when he was overcome by a trance that caused him to become lost from his parents for hours. The experience was so strong that Argento never forgot it and immediately thought of it when he came across Magherini's book, which would become the basis of the film.
The painting that Anna literally steps into is a Rembrant painting of 17th Century policemen, entitled 'Night Watch'. The painting that causes Anna to faint in the museum is by Brueghel, it's called 'Landscape with the Fall of Icarus'.
The footage of Anna underwater after fainting in the gallery was actually shot in the sea - not a swimming pool. The huge grouper fish that Anna kisses was a remote model that was being pulled through the waters by cables attached to a small float on the oceans surface. Mere moments after wrapping the underwater shoot, the fish stopped working.