"Evelyn Underhill (6 December 1875 – 15 June 1941) was an English Anglo-Catholic writer and pacifist known for her numerous works on religion and spiritual practice, in particular Christian mysticism. . . . Since 2000 the Church of England commemorates her liturgically on 15 June." (Wikipedia).
Below is an excerpt from Evelyn Underhill's 1911 book called, "Mysticism: A Study in the Nature and Development of Man's Spiritual Consciousness." Methuen & Co Ltd. Pg. 381-383.
"The "Dark Night of the Soul," once fully established, is seldom lit by visions or made homely by voices. It is of the essence of its miseries that the once-possessed power of orison or contemplation now seems wholly lost. The self is tossed back from its hard-won point of vantage. Impotence, blankness, solitude, are the epithets by which those immersed in this dark fire of purification describe their pains.
Psychologically considered, the Dark Night is an example of the operation of the law of reaction from stress. It is a period of fatigue and lassitude following a period of sustained mystical activity. "It is one of the best established laws of the nervous system," says Starbuck, "that it has periods of exhaustion if exercised continuously in one direction, and can only recuperate by having a period of rest." However spiritual he may be, the mystic—so long as he is in the body—cannot help using the machinery of his nervous and cerebral system in the course of his adventures. His development, on its psychic side, consists in the taking over of this machinery, the capture of its centres of consciousness, in the interests of his growing transcendental life. In so far, then, as this is so, that transcendental life will be partly conditioned by psychic necessities, and amenable to the laws of reaction and of fatigue. Each great step forward will entail lassitude and exhaustion for that mental machinery which he has pressed unto service and probably overworked. When the higher centers have been submitted to the continuous strain of a developed illuminated life, with its accompanying periods of intense fervour, lucidity, deep contemplation—perhaps of visionary and auditive phenomena—the swing-back into the negative state occurs almost of necessity.
This is the psychological explanation of those strange and painful episodes in the lives of great saints---indeed, of many spiritual persons hardly to be classed as saints---when, perhaps after a long life passed in faithful correspondence with the transcendental order, growing consciousness of the "presence of God," the whole inner experience is suddenly swept away, and only a blind reliance on past convictions saves them from unbelief. The great contemplatives, those destined to attain the full stature of the mystic, emerge from this period of destitution, however long and drastic it may be, as from a new purification. It is for them the gateway to a higher state. But persons of a less heroic spirituality, if they enter the Night at all, may succumb to its dangers and pains. This "great negation" is the sorting-house of the spiritual life. Here we part from the "nature mystics," the mystic poets, and all who shared in and were contented with the illuminated vision of reality. Those who go on are the great and strong spirits, who do not seek to know, but are driven to be.
We are to expect, then, as a part of the conditions under which human consciousness appears to work, that for every affirmation of the mystic life there will be a negation waiting for the unstable self. Progress in contemplation, for instance, is marked by just such an alteration of light and shade: at first between "consolation" and "aridity"; then between "dark contemplation" and sharp intuitions of Reality. So too in selves of extreme nervous instability, each joyous ecstasy entails a painful or negative ecstasy. The states of darkness and illumination coexist over a long period, alternating sharply and rapidly. Many seers and artists pay in this way, by agonizing periods of impotence and depression, for each violent outburst of creative energy.
Rapid oscillations between a joyous and a painful consciousness seem to occur most often at the beginning of a new period of the Mystic Way: between Purgation and Illumination, and again between Illumination and the Dark Night: for these mental states are, as a rule, gradually not abruptly established. Mystics call such oscillations the "Game of Love" in which God plays, as it were, "hide and seek" with the questing soul."