Some signs that I've experienced:
* Hearing non-existent voices, or at least feeling that supernatural spirits are talking to me.
* "Loud thoughts" that don't feel like they belong to me (Bipolar Disorder Thought Types | Breaking Bipolar)
* Psychosis: e.g. I was certain that I had a mute pet dog made of white fire. His name was Gödel. Or feeling that I had leaves and vines growing out of my body.
* Head fills with incoherent noise. There's a broken radio in there. The noise warps and froths and frizzes.
* More psychosis: seeing the floor melt and bubble and steam.