How can an anaesthetic be so psychedelic?
This is down to the way that Ketamine works on the brain. As it disconnects your brain from your body, the mind takes over with its imagination. Ketamine has been compared to a waking dream. Enthusiasts claim that when you no longer have the interference of every day bodily sensations, you open up unused senses and spiritual insights. You can find some detailed explanations of brain effects here.
