The strongest d** are the ones most like ordinary brain chemistry, the most extreme case being DMT. DMT only lasts seven to ten minutes and yet it's the most profound dislocation of reality that you can undergo.
I thought I knew a lot about psychedelics before I encountered DMT and it showed me that I knew virtually nothing and I took three, four, very large inhalations. My impression was of falling forward through some kind of tube that was fluctuating. This space was filled with beings, entities, of some sort. Creatures who've made it light, and they were jumping in and out of my chest and I thought I must have died. This couldn't happen to somebody, and come back.
You cannot go further than this into the bardo and return. The shaman is someone who has seen the beginning and the end. It's the most challenging, enlightening, astonishing, terrifying, joyous, strange thing in the world. I don't mean to scare anyone off but these are bizarre dimensions of extraordinary power and beauty. People should be very careful.