When I close my eyes, even if I happen to be in a perfectly dark room, my visual field contains fuzzy patches of colour, sort of like an afterimage of a christmas tree without the tree, and persistent. Sometimes the fuzzy patches are blue other times they are orange. I used to think this must be universal, but now I have significant doubts about that.

Yes, I see things like that, too.

Also, if I stare at the walls of a dimly lit room for long enough, especially when I am tired, the room seems to 'shift' or shake around me somehow. This is only a rough description, because the words to precisely describe the 'transformation' of the walls around don't really exist in English.

Yeah, I think I've felt something like that, although it's pretty rare for me to experience it. It's a little like when you're feeling dizzy because you've been spinning...