The biggest delusion is Hyper-normality, most of the western world suffer from this on a mass scale. We have become detached from ourselves spiritually. Say what you want about religion but spirituality can be a key factor in people's lives without follows religion, Sam Harris has a book on it "Spirituality without religion. Psychosis is normally the tem used for a person who is experiencing delusions, yet psychiatry is any everyone else who has never experienced psychosis is seeing it from a third person perspective in which they can only judge by observation and label it as illness/disease/disorder. Psychosis/mania and the mind is a lot more complex than most psychiatrists think. A person with psychosis is experiencing a higher level of consciousness, same goes for mania. In shamanic tradition they induce these states and they call what we call psychosis; "the spirit world". When one is experiencing these higher states they are in a kind of spirit world, everything seems confusing to them and they become overwhelmed, thoughts become disordered because they do not know what they are experiencing. It takes a shaman up to 20 years to master these states, live and function within them and use them to their advantage. Bipolar in order also teaches people this.