I'm not a doctor but the nightmares sound more like a trauma response than psychosis to me. It's perhaps an idea to see about some counselling or other talk therapy. Your mood symptoms and social withdrawal could just be because psychosis is a scary thing and then spending time in hospital can shake you up a bit. Make you feel a bit timid, down etc.

If I were you I would consider reaching out to a GP or find counselling of some kind in your area