Saints Barsanuphius and John. "Guidance Toward Spiritual Life."

Q: I have heard that if one and the same dream appears to someone three times, one should recognize it as true; is this so, my Father?

A: No, this is wrong; such a dream also one need not believe. He who has appeared once to anyone falsely can do this three times and more. Watch, lest you be put to shame (by the demons), but pay heed to yourself, brother.

Q: Tell me, Master, how can the devil dare in a vision or a fantasy during sleep to show the Master Christ or Holy Communion?

A: He cannot show the Master Christ Himself, nor Holy Communion, but he lies and presents the image of some man and simple bread; but the holy Cross he cannot show, for he does not find means of depicting it in another form.

Inasmuch as we know the true sign and image of the Cross, the devil does not dare to use it (for our deception); for on the Cross his power was destroyed, and by the Cross a fatal wound was given him. The Master Christ we cannot recognize by the flesh, which is why the devil tries to convince us by lying that it is He, so that having believed the deception as if it were truth, we might perish. And thus, when you see in a dream the image of the Cross, know that this dream is true and from God; but strive to receive an interpretation of its significance from the Saints, and do not believe your own idea. May the lord enlighten the thoughts of your mind, O brother, so that you might escape every deception of the enemy.

http://www.orthodox.net/gleanings/dreams.html

Saint John Cassian. "Conferences".

The Second Conference of Abbot Moses. On Discretion.

Chapter VIII. Of the fall and deception of a monk of Mesopotamia.

It is a long business too to tell the story of the deception of that monk of Mesopotamia, who observed an abstinence that could be imitated by but few in that country, which he had practised for many years concealed in his cell, and at last was so deceived by revelations and dreams that came from the devil that after so many labours and good deeds, in which he had surpassed all those who dwelt in the same parts, he actually relapsed miserably into Judaism and circumcision of the flesh. For when the devil by accustoming him to visions through the wish to entice him to believe a falsehood in the end, had like a messenger of truth revealed to him for a long while what was perfectly true, at length he showed him Christian folk together with the leaders of our religion and creed; viz., Apostles and Martyrs, in darkness and filth, and foul and disfigured with all squalor, and on the other hand the Jewish people with Moses, the patriarchs and prophets, dancing with all joy and shining with dazzling light; and so persuaded him that if he wanted to share their reward and bliss, he must at once submit to circumcision. And so none of these would have been so miserably deceived, if they had endeavoured to obtain a power of discretion. Thus the mischances and trials of many show how dangerous it is to be without the grace of discretion.

Saint Nikitas Stithatos. "On the Inner Nature of Things and on the Purification of the Intellect: One Hundred Texts". From Philokalia, Vol. 4.

60. Those who have attained spiritual maturity can also analyze, the impulsions and proclivities of the soul, and can guide and guard their inner state, on the basis of dreams. For bodily impulsions and the images in our intellect depend upon our inner disposition and preoccupations. If your soul hankers after pleasure and material things, you will dream about acquiring possessions and having money, about the female figure and sexual intercourse - all of which leads to the soiling and defilement of soul and body. If you are haunted by images of greed and avarice, you will see money everywhere, will get hold of it, and will make more money by lending it out at interest and storing the proceeds in the bank, and you will be condemned for your callousness. If you are hottempered and vicious, images of poisonous snakes and wild beasts will plague you and overwhelm you with terror. If you are fall of self-esteem, you will dream of popular acclaim and mass-meetings, government posts and high office; and even when awake you will imagine that these things, which as yet you lack, are already yours, or soon will be. If you are proud and pretentious, you will see yourself being carried along in a splendid coach and even sometimes airborne, while everyone trembles at your great power. Similarly, if you are devoted to God, diligent in the practice of the virtues, scrupulous in the struggle for holiness and with a soul purged of material preoccupations, you will see in sleep the outcome of events and awe-inspiring visions will be disclosed to you. When you wake from sleep you will always find yourself praying with compunction and in a peaceful state of soul and body, and there will be tears on your cheeks, and on your lips words addressed to God.

Saint John Climacus. "The Ladder of Divine Ascent". Step 3.

Concerning the dreams of novices

Our mind is the instrument of knowledge, but it is very imperfect and filled with all sorts of ignorance. This is a fact that cannot be disguised.

Now the palate discriminates between various kinds of food, the hearing distinguishes between the things it perceives, the sun shows up the weakness of the eyes, and words reveal the ignorance of a soul. Nevertheless, the law of love urges us to reach beyond ourselves, and so it seems to me—and I do not wish to be insistent—that, immediately after this discussion of exile, or rather, in the course of it, something ought to be said about dreams. For we should not be unaware of this type of deceit practiced by our wily enemies.

A dream is a stirring of the mind during the body's rest, while a fantasy is something that tricks the eyes when the intellect is asleep. Fantasy occurs when the mind wanders, while the body is awake. A fantasy is the contemplation of something that does not actually exist.

St Diadochos of Photiki. "On Spiritual Knowledge and Discrimination. One Hundred Texts". From Philokalia, Vol. 1.

37. The dreams which appear to the soul through God's love are unerring criteria of its health. Such dreams do not change from one shape to another; they do not shock our inward sense, resound with laughter or suddenly become threatening. But with great gentleness they approach the soul and fill it with spiritual gladness. As a result, even after the body has woken up, the soul longs to recapture the joy given to it by the dream. Demonic fantasies, however, are just the opposite: they do not keep the same shape or maintain a constant form for long. For what the demons do not possess as their chosen mode of life, but merely assume because of their inherent deceitfulness, is not able to satisfy them for very long. They shout and menace, often transforming themselves into soldiers and sometimes deafening the soul with their cries. But the intellect, when pure, recognizes them for what they are and awakes the body from its dreams. Sometimes it even feels joy at having been able to see through their tricks; indeed it often challenges them during the dream itself and thus provokes them to great anger. There are, however, times when even good dreams do not bring joy to the soul, but produce in it a sweet sadness and tears unaccompanied by grief. But this happens only to those who are far advanced in humility.