The opening for Vertigo is "book-ended" with the film's conclusion. They both "hang" there. The film redounds upon itself, like a cyclic force, like vertigo: one of the reasons why some people find themselves returning to this film again and again.
One of the things that's so great about the opening of Vertigo is it doesn't give you any information, then or later, how Jimmy Stewart gets off the rooftop.
The film has a strong moral lesson about obsession.