These are old terms. I think "neurosis" came from psychoanalysis and is used to describe an inner conflict morphed into behaviour. The term (for me) is dangerous because it draws the clinicians attention toward the individual and away from the person's context, toward the past and away from present time situations. "Psychosis" is a word nobody ever agreed on. I think it just means you're nuts. Psychiatrists use it to mean a person is unable to care for themselves because of an intrusion of hallucinations, delusional perceptions, etc. Once again, I fear this word because it may lure the therapist into only considering the skin bound person, not the overall context and what responses psychotic behaviour may be inviting. I do use this word when talking generally about a person and I'm being lazy, but I prefer to speak of specific phenomena like "a voice says..." or "the perception that...". Someone said neurotics build castles in the sky, psychotics live in them, and psychiatrists collect the rent.