Did you get all that? OK, because that one-minute scene just told you the entire movie. The shots are too fast to see, but if you keep your finger firmly pressed on your pause button (or watch this handy frame-by-frame version), you can see weird stuff like Nina being stalked by the characters of the ballet, including the one she plays:
Well, hopefully the continuity person got fired over this mishap.
Or Nina dancing with the theater director, who isn't actually in the club at all. Adding to the confusion, he later morphs into Rothbart, Swan Lake's feathery villain. This represents his negative influence on Nina.