There are some people who have tremendous insight into the nature of reality as vast and wonderful—what is sometimes called sacred outlook—but then they become completely dissatisfied with ordinary life. Rather than that glimpse of sacred outlook actually enriching their life, it makes them feel more poverty-stricken all the time. Often the reason that people go from neurosis into psychosis is that they see that spaciousness and synchronistic situation and how vast things are and how the world actually works, but then they cling to their insight and they become completely caught there. It has been said, quite accurately, that a psychotic person is drowning in the very same things that a mystic swims in.
From The Wisdom of No Escape and the Path of Loving-Kindness by Pema Chödrön, page 76