I am so new to this...I am trying to learn, but I am confused about psychosis. What do you experience when you are having psychosis? What are the early signs? how do you stop it? what is the difference between psychosis and being highly sensitive?

I am reading a book by Julie Fast but the descriptions are not specific enough for me to understand, though I am trying. I also read somewhere that having something repeat in your head is an early sign and I don't get that at all because people get songs stuck in their heads all the time. Maybe I am not understanding what I am reading.