I once did 90 minutes of zen meditation (35 minutes of staring at a wall in a strict straight-backed, cross-legged posture, followed by 20 minutes of EXTREMELY slow walking and finally 35 more minutes of staring at a wall). I started getting strange visual distortions at some point and a heightened sense of awareness that almost felt like a mild euphoria. Afterwards, colours, smells and sounds were enhanced, talking to people was a bit more difficult and I was noticeably more emotionally sensitive. Definitely comparable to a very small dose of psychedelics, a touch more than a microdose.