When you hear things and see visions and there is no stimulus to trigger that, it is a hallucination. When you have a stimulus and perceive it wrongly due to mental conditions, it is an illusion. When you have a stimulus and perceive it wrongly and...

I had a tough time choosing the best one to put here. Finally, settled on the one you see above -- here is an underwater scene with little fishes floating around a mysterious little staircase. Okay, now before I get too carried away, lemme tell...