>>16775994 (OP)
Im a neuropsychopharmacology midwit.
For the visions:
Since 5HT2A-agonists or partial agonists (e.g. 2C-B) kinda inhibit your visual processing, you're observing a more raw and uncalibrated version of (visual) input,where your brain is less able to see the set of all different things (note that observing someTHING already includes your brain's interpretation of raw visual data) and more likely to see the underlying "oneness", by which I mean nothing more than the bright spots of different colors in different shapes and sizes that raw visual data is (even colors are a human concept but that's beyond our scope here).
Now close your eyes and rub them firmly. You will begin to see, albeit less colorful and alive, the exact same forms and abstract geometric figures that you see on psychedelics.
So I suppose that the strange visions arise from inhibited visual processing that forces the brain into its "default visual mode" consisting, at least in humans, of those kinds of radially symmetric geometric forms.
As for the thoughts, I would say that it follows a similar mechanism of disruption of the usual homeostasis in the brain that results in different brain activity for the same input. It has been proven that acute psychedelic usage increases connectivity between brain areas that are normally less connected
