Picture taken from this site.
Every thought, fantasy, emotion, is an event in the world.
Realizing that world is just a dream, is not an event in the world, because it relates to the world as a whole, therefore it cannot be lost as a result of any event (e.g.: brain damage).
A paradox: one dramatically misses the point when one tries to analyze it, because writing the sentence above (in italics), or even thinking of it, is already an event in the world.
When one puts aside all concepts, imaginations, desires (by not clinging to any of them), all that remains is the lasting happiness of Dreamer.