Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter II. An investigation of the origin of a sudden change of feeling from inexpressible joy to extreme dejection of mind.

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Chapter II.

An investigation of the origin of a sudden change of feeling from inexpressible joy to extreme dejection of mind.

So then we asked this blessed Daniel why it was that as we sat in the cells we were sometimes filled with the utmost gladness of heart, together with inexpressible delight and abundance of the holiest feelings, so that I will not say speech, but feeling could not follow it, and pure prayers were readily breathed, and the mind being filled with spiritual fruits, praying to God even in sleep could feel that its petitions rose lightly and powerfully to God: and again, why it was that for no reason we were suddenly filled with the utmost grief, and weighed down with unreasonable depression, so that we not only felt as if we ourselves were overcome with such feelings, but also our cell grew dreadful, reading palled upon us, aye and our very prayers were offered up unsteadily and vaguely, and almost as if we were intoxicated: so that while we were groaning and endeavouring to restore ourselves to our former disposition, our mind was unable to do this, and the more earnestly it sought to fix again its gaze upon God, so was it the more vehemently carried away to wandering thoughts by shifting aberrations and so utterly deprived of all spiritual fruits, as not to be capable of being roused from this deadly slumber even by the desire of the kingdom of heaven, or by the fear of hell held out to it. To this he replied.