When the author wants to take a break from the current storyline or reveal some piece of vital information, the story may enter a dreamatic interlude, a period of time the protagonist spends in his or her own head, with the readers participating in their imagined actions. Often this will happen at a dramatic peak in the story, especially when something possibly deadly has just happened to the protagonist. Other times it will be used to create suspense or attempt to blur the line between real events and imagined ones.
Examples[]
Alanna appeared to have been killed, only to enter a dreamlike world resembling her house. It seemed to be directing her to eat a cake.
Samuel has several, of the "blurring the line between real and imagined" variety. Usually they are accompanied by red text giving him vague directives.
Crystal Raver seems to have been smothered in a lava flow. He then seemed to relive a (possibly) altered version of events from his childhood.
Marek Larson enters a vision when he passes out in the cold, which granted physical benefit for some reason. Later, Marek passes out after devouring a talking mushroom, inducing a vision where he is a cyborg scout working for a robot corporation.
The story thrives on this trope, and it is unclear until the end (and not even then, one could argue) which events actually occurred and which ones are part of a dream.