I'll take a shot at it -

In dreams unlike in movies, you experience feelings directly. Movies consist only of visuals and sound. But dreams, being generated inside your own mind and made of the stuff of the mind, consist of directly experienced thoughts, feelings, memories - anything you can experience in your mind when awake really. Sometimes for instance you experience great fear for no real reason, or elation. Sometimes you know things - like that you have to accomplish some task before a certain time. There's no concept of HOW you know these things - it's just a sort of implanted thought or memory.

So a dream can implant or generate a feeling that a lot of time has been passing. Just as it can generate the feeling that you're dead and rotting, or that you're a glowing being made of light. Or really any other feeling or idea you could possibly imagine.