Shock Rating
PG
Although Alfonso Cuarón directed the very NC-17 film Y Tu Mamá También prior to Azkaban, we stay firmly in PG territory here.
Hormones haven't yet gone wild at Hogwarts, although we do glimpse a bit of a budding romance between Ron and Hermione. The Dementors are pretty intense, but as long as you don't think too long about what it would be like to have your own soul sucked out and never be happy again, they won't give you nightmares.
(Um, we'll be sleeping with the lights on.)