Do they remain in the air for a while then pop up in someone else's head, do they disappear for good, or does something else happen?
I love this as a #worldbuilding exercise, like somewhere there's a planet populated by half-baked ideas for creatures, monsters from children's imagination, discarded characters from novels and long forgotten imaginary friends.
They would have the most fantastic buildings, culture and technology we could dream of (and have).
What would that place look like? What would they eat and what is their main source of entertainment? What are the kind of problems the inhabitants would have?