Specifically addressing devotees’ visions of the Lord and the saints, Bishop Ignatii points out that human imagination can lead to fake sensory experiences, falsely recognized by the person as originating outside of his or her mind…
Guard yourself from imagination, which can make you fancy that you see the Lord Jesus Christ, that you touch and embrace Him. This is empty play of puffed-up and proud self-opinion! This is deadly self-praise!
If during your prayer there appears to your senses or spontaneously in your mind an image of Christ, or of an Angel, or of any Saint—in other words, any image whatsoever—do not accept this apparition as true in any way, do not pay any attention to it, and do not enter into a conversation with it. Otherwise, you will surely suffer deceit and most serious damage to your soul, which has happened to many.
Imagining the Lord and his saints gives to the mind as if materiality, leads it to the false, prideful opinion of self—leads the soul into a false state, a state of deceptive self-praise.
In other words, according to Bishop Ignatii, purposefully creating images in one’s mind, and even accepting those appearing spontaneously, is not only dangerous spiritually, but can also lead to the damage of the soul, or psychological problems, “which,” he says, “has happened to many.”
Undoubtedly, here Ignatii refers to the spirituality of some Western saints, “Do not play with your salvation, do not. Take up the reading of the New Testament and the Holy Fathers of the Orthodox Church, but not of Teresa and other Western crazies…”
But cases of mental disorders facilitated by improper prayer or state of mind are also mentioned in various Orthodox literature, especially paterikons.