A little background:
Eclipse Phase has a drug in the setting that creates a shared hallucinated experience among participants. These drugs, called Petals, are also designed to have some sort of narrative beyond them- think shared LSD trip with some overarching theme. Generally these trend towards something pretty dark.
While this is a fairly system specific question, the answers don't really need to be. I think a lot of GMs have probably had similar experiences running shared dreams or the like.
I'm looking for specific advice and considerations about how to design something that will feel otherworldly and exotic to the players. How do you go about designing an encounter or series of encounters like that?