I'll give it a go!
Ketamine is a dissociative anaesthetic, often painted by the press as a "horse tranquilliser" but in fact used in small children and on battlefields because it's much safer than many other anaesthetics to get the dosage wrong. But the side effects are pretty mind-blowing for a human adult.
A recreational "line dose", also known as "the K-hole", basically knocks you unconscious and then "lets you watch" as your consciousness returns. I scare-quote "lets you watch" because each word in that phrase is also a concept that you need to work out from first principles as you rediscover:
- Something exists (pure being / presence)
- There is a point of view (a "me" or a witness)
- Space appears (here / there)
- Time appears (before / after, continuity)
- Agency appears (I can do / something can do)
- Other minds appear (not alone; others exist)
- Objects appear (room, body, people, language)
- Narrative identity returns ("Oh right, I'm me, I took ketamine, I'm safe")
...which is why it's crucial to be in a good "set and setting" when you take it.
The experience is an extremely spiritual one because the concepts arrive in an order to which they are literally foundational to your normal experience. As your emerging consciousness tries to reintegrate its sensory input (or as subsystems come back online into the maximally integrated causal structure or "dominant complex" of Integrated Information Theory) you are still trying to make sense of space (which appears geometric because your cognitive systems are trying to collapse it into a comprehensible structure despite being partially offline) and time (which loops because your brain's normal mechanisms for sequential prediction and memory are disrupted) while you rediscover other minds which are foundational to meaning, morality, love and the human condition.
It can be quite addictive and harmful to your bladder if over-used, so I've only ever taken it a few times. I intend to take it again, but only very sparingly as I've encountered people who have definitely overdone it.
I intend also to try DMT, which is the most psychoactive ingredient in Ayahuasca (but without all the emetic stuff) and related to shrooms (psilocybin is 4-PO-DMT, psilocin is 4-HO-DMT). It's apparently now possible to get it in freebased form for vapourising, but I haven't sourced this yet.