"Psychosis is a condition that affects the way your brain processes information. It causes you to lose touch with reality. You might see, hear, or believe things that aren’t real. Psychosis is a symptom, not an illness. A mental or physical illness, substance abuse, or extreme stress or trauma can cause it." Maybe it would be more precise if the above definition specified reality as "waking reality", and used the word "use" instead of "abuse" (after all, more often than not the application of particular substance is intentional). Otherwise, I think, it's spot on. Yes, it is defined by hallucinations, delusions, and/or disorganization, but psychotic experience can be as much transformative as it can lead to "madness". That's the main difference between a shaman and a junkie, or a mystic and a crazy "fundamentalist".