I think hallucinations need to be discussed. There are all sorts of hallucinations, and then many sorts which are okay, like the ones I think which most of us have in bed at night before we fall asleep, when we can see all sorts of patterns or faces and scenes.

In general, people are afraid to acknowledge hallucinations because they immediately see them as a sign of something awful happening to the brain, whereas in most cases they're not.

With any hallucinations, if you can do functional brain imagery while they're going on, you will find that the parts of the brain usually involved in seeing or hearing - in perception - have become super active by themselves. And this is an autonomous activity; this does not happen with imagination.

Oliver Sacks Quotes