St. Ignatius (Brianchaninov). "On prelest". About Night Dreams.
Demons use dreams to disturb and injure human souls. Likewise, inexperienced monks, by paying attention to their dreams, harm themselves. It is therefore essential here to determine the exact significance of dreams in a person whose nature has not yet been renewed by the Holy Spirit.
During sleep, the state of a sleeping person is so designed by God that the whole man is in complete repose. This repose is so complete that a person loses consciousness of his existence and is in a state of oblivion or self-forgetfulness. During sleep, all voluntary activities and labour governed by the will and reason stop. Only that activity continues that is essential for existence and cannot be relinquished. In the body, the blood continues its circulation, the stomach digest food, the lungs maintain respiration, the skin perspires. In the soul, thoughts, fantasies, and sensations continue to be produced, only without dependence on the will and reason, but by the action of our unconscious nature.
A dream consists of such fantasies accompanied by their peculiar thoughts and sensations. It often seems strange, as if it bore no relations to the person's voluntary and purposeful thoughts and imaginings, but appears spontaneously and whimsically in accordance with a law and demand of nature. Sometimes a dream bears an incoherent impression of voluntary thoughts and fancies, while sometime is a result of a particularly moral state of mind. Thus, a dream in itself cannot and should not have any significance. The desire of certain people to see in the ravings of the dreams a prediction of their future or the future of others or some other meaning is ludicrous and quite illogical. How can that be which has no cause for its existence?