Long before the idea of “mid-life crises” became part of our modern nomenclature, there have been men and women throughout the ages who have undergone some tough, emotional and psychological—and spiritual—crises. Sixteenth-Century Spanish mystic, St. John of the Cross, called this period “the dark night of the soul.” Evelyn Underhill, in her 1911 book, Mysticism, said this period of time “is a deeply human process.” In this passage, Underhill describes the process.
The self, in its necessary movement towards higher levels of reality, loses and leaves behind certain elements of its world, long loved but now outgrown: as children must make the hard transition from nursery to school. Destruction and construction here go together: the exhaustion and ruin of the illuminated consciousness is the signal for the onward movement of the self towards other centres: the feeling of deprivation and inadequacy which comes from the loss of that consciousness is an indirect stimulus to new growth. The self is being pushed into a new world where it does not feel at home; has not yet reached the point at which it enters into conscious possession of its second or adult life.
For further exploration: Mysticism