I ate a shitload of hash once and saw some cool shit. Like when I turned my head there was a strobe-light effect, without the light. Not really a hallucination but fun. I saw some colours on the ceiling in a dark room, but probaly best of all my attention drifted away and I started playing a video-game in my head, like a 2-d side scroller. I was only imagining it, I didn't actually see anything outside my head, but my sub-conscience made up the game as I went along (controlling the character, I think, memorys a little fuzzy), so I had no idea what was coming up in the level. Plus it had a soundtrack of my thinking-voice saying meaningless words repeatedly. So basic your everyday experience .