When you are having a psychedelic experience, relaxed, and you start daydreaming. Except that, instead of a normal, passive daydream, you actually slip into the reality you imagine, sometimes quickly and without notice, believing in what you imagine to be physically interactable. It's like a typical dream, except everything feels very fresh and vivid, and you're typically lucid enough to get out of it in a flash if you need to. Returning from a psychedelic daydream will leave you mystified and refreshed. All it takes is relaxation and the psychedelic will guide you into your imagination. Many psychedelic users are not aware of how easy this is because they are typically submerged in physical activity, whether by themselves or with others, not allowing their brainwaves to slow enough until they crash (fall asleep).
I had a Psychedelic Daydream yesterday. It was incredible, I really thought I was back on the beach!