How our fifth combat is against the spirit of dejection, and of the harm which it inflicts upon the soul.
In our fifth combat we have to resist the pangs of gnawing dejection: for if this, through separate attacks made at random, and by haphazard and casual changes, has secured an opportunity of gaining possession of our mind it keeps us back at all times from all insight in divine contemplation, and utterly ruins and depresses the mind that has fallen away from its complete state of purity. It does not allow it to say its prayers with its usual gladness of heart, nor permit it to rely on the comfort of reading the sacred writings, nor suffer it to be quiet and gentle with the brethren; it makes it impatient and rough in all the duties of work and devotion: and, as all wholesome counsel is lost, and steadfastness of heart destroyed, it makes the feelings almost mad and drunk, and crushes and overwhelms them with penal despair.
Source: Institutes (New Advent)