Did you read the wiki I linked to? it strikes me you only have the basic understanding of what a hallucination is or can be.
have you seen any TED talks by Dr Oliver Sacks?
Have you read this? http://www.skeptic.com/downloads/why-people-see-ghosts.pdf
Have you read Carl Sagans Demon Haunted World?
Do you really want to find out what happened? Some dont because it will crush their world view of gods and spirits.