just another thought on movie material, OP:
opinion is split, but I remember it having quite a full on visual style. Could be worth a look.
Other than that, have you played Batman: Arkham Asylum?
There's a couple of levels/sections that are inside Batman's psyche, care of Scarecrow. Very nifty stuff.
Another thought, if you're designing the "levels" around a central mental illness concept, look at books/films/whatever that deal with similar themes.
For example: Paranoia
1984 is THE classic paranoid, dystopian fiction.
So, for a level based around Paranoia make it like Airstrip one: cold, harsh, soviet bloc type architecture, lots of plain concrete, cold winds, etc. Keep it relevant to the time period; e.g. in a modern period, have cameras everywhere, in the 1950s, have cops on every corner, and they're all looking menacingly at the characters.
It might seem obvious, but the descriptions of the details will be distracting to the players, and it's unlikely they'd immediately make the connection between eyes/cameras/police and paranoia.