I did mushrooms once to see if it would help with my depression (no, unfortunately) and what I think happened was I was looking at a rug and thought it looked like a duck. And the thought process was that the shapes and colors and patterns were all things you'd find on a duck, even though the rug as a whole had nothing obviously duck like about it. With no basis i think the shrooms kind of turned off or altered some parts of my brain's pattern recognition and had me seeing mundane things in a totally novel way. I don't recall any halucinations, just seeing day to day things with utter fascination as I saw things about them that i'd never seen before.

I did a series of ketamine treatments (also for depression, also failed sadly) and a steady dose of iv ketamine administered over an hour is pretty wild. The sense of timelessness and distance from your life at the height of the drug's effects is strange, I don't have a better word. I found it gave me a lot of space for introspection, like my life was an object I could look at and turn around and examine. I also brought music for a couple of sessions. "The Wall" pairs very well with ketamine, which is the least surprising thing ever.