Did anyone notice that he gets given a mushroom before everything starts going trippy? There's also a lot of mushroom imagery in the OP too.
Also to add to this, whenever I take mushrooms I always notice small things, like writing and stuff that seems connected and brings on a small sense of paranoia (Similar to when Sasami starts seeing the word 'Choco' everywhere). Then suddenly my trip explodes into bizzare dripping dali-esque visuals and general psychedelic experiences, very similar to how the chocolate floods everywhere and suddenly everyone starts acting bizzarely out of character.Mmmhm, I think that's kind of important to remember.
Also the fact that when tripping, surfaces seem to seem almost like liquid as if they are dripping or made of a strange material...the overly saturated colors seem very reminiscent of a mushroom or LSD trip too. I know Japan is reasonably familiar with magic mushrooms as they've taken them for centuries and they weren't made illegal until 2002 or 2003.