The Life of St Theodosius provides us with an example of this. Some monks had turned from the right path by the practice of an aberrant and badly understood form of asceticism and above all in these efforts had placed their confidence in themselves rather than God. As a result they were overcome with psychic difficulties through the activity of Satan. St Theodosius welcomed them into his monastery to care for them. St Theodore of Petra provides us with a similar case:

A number of men in the mountains and in the caves had not led the struggle for a Christian life according to Christ, and, for having practiced a rash form of asceticism with great zeal, were pierced through by the sword of pride. They had attributed their ascetic activities to their own strength and had forgotten that our Lord had said: Without me, you can do nothing (John 15:5). Because of this wasting of the flesh, or having in some way fallen under the judgment of God which surpasses understanding, they were delivered up to Satan, and because of their deranged minds they could no longer control their thoughts.

Mental Disorders & Spiritual Healing: Teachings from the Early Christian East
Jean-Claude Larchet

We have previously devoted a lengthy study to the subject of spiritual maladies. As a result, we will limit ourselves in this work to merely recalling the analysis of the passions of acedia and sadness—their links with the various forms of depression are quite obvious and, in recent years, have attracted the attention of some psychiatrists who have shown themselves quite sensitive to the depth, richness and wisdom of Patristic analysis.

These last mentioned illnesses have an exemplary value. All the more so as symptoms of anxiety and depression afflict over two hundred million individuals, who most often receive only chemical treatment for their illness. Undoubtedly some of these are organic in origin and, as such, this therapy is justified. However, most of them, as is generally admitted, are suffering from what is currently called ‘mal de vivre’ (feeling lousy’). In other words they suffer from existential problems which standard psychiatry remains totally incapable of treating. It is obvious that these problems to a great extent relate to the spiritual sphere as envisioned by the Fathers whose nosology and therapeutic techniques would appear to be most pertinent, for despite the fact that both time and social context are different, they touch upon universal dimensions of human existence, upon difficulties that afflict everyone who desires to find a meaning for existence and to harmonize their interior life; individuals who wish to conform their activities to values whose disappearance, as many psychiatrists and psychologists admit, leads to the increase of mental problems, especially anxiety and depression.

Mental Disorders & Spiritual Healing: Teachings from the Early Christian East
Jean-Claude Larchet

Aggression, also found in the majority of neurotic states and in certain psychoses, can be connected with the passion of anger in the broader sense given to this term by the Fathers. Asthenia or lethargy, common to many mental diseases, corresponds rather exactly to one of the essential components of the passion of acedia. One can also perceive a direct connection between standard neurotic phobias, defined as ‘agonizing fears, with the passion of fear. The neurosis of anxiety can be easily classified within the framework of this same passion of fear and the passion of sadness. Psychotic depression has a connection on the one hand with acedia and on the other with despair, an extreme form of the passion of sadness.

Mental Disorders & Spiritual Healing: Teachings from the Early Christian East
Jean-Claude Larchet

The eye of the despondent one stares constantly at the window, and his mind presents visitors to him. The door creaks, and he jumps up; he hears a voice, and peers through the window, and he does not go away from there, until, exhausted, he sits down. If the despondent one reads, then he yawns a great deal, and soon he sinks into sleep. He rubs his eyes, and stretches out his hands, and while his eyes wander from the book, he stares at the wall, then he turns away again, and reads a little, and when he leafs through [the book], he searches for the end of the exposition. He counts the pages, and determines the number of sheets, finds fault with the writing and the design and in the end he snaps the book shut. He lays his head on it, and falls into a not-too-deep sleep, and in the end hunger wakes up the soul again, and the soul [now renewed] attends to its own concerns.

Despondency
Gabriel Bunge

Despondency: breezy love, tramper of steps, hater of love of work, fight against solitude, thunderstorm of psalmody, aversion to prayer, slackening of asceticism, ill-timed slumber, sleep, tossing and turning, burden of solitude, hatred of the cell, adversary of ascetical efforts, counter-attacking against endurance, impediment to reflection, ignorance of the Scriptures, companion of sadness, daily rhythm of hunger.

—Evagrius Ponticus

Despondency, Gabriel Bunge

Believe me, brother, that boredom, accidie, sluggishness, irritation, mental fatigue and the other causes of distress that the enemy of righteousness inflicts upon ascetics, are all with divine permission. If man puts up with them patiently and without buckling, they will be rendered to him as a pure oblation and a holy accomplishment—provided he is free from pride and vanity.

—St Isaac the Syrian, in “The Four Books,” 1.5.92—94

Incidentally, it is astonishing to see how, in the beginning, man was tempted by pride: he wanted “to be like God” (Gen 3:5); in other words, he wanted to become God without God or against God. That was presumption. Today we are witnessing the opposite temptation: people think it would be better not to exist; this is faint-heartedness.

Two reactions are possible then: losing the sense of time, both past and future, as nihilism does; or else, on the contrary, fleeing the present and taking refuge in the past or in the future.

As a reaction to the gloominess of the present there may indeed be a tendency to cultivate an excessive nostalgia for the successful, well-spent moments of the past. To embellish it, to delight in it, to tell stories about it. When nothing goes well any more in the present, it is so reassuring to become attached to the past, when one “did so many good things”. Then, one tells stories…to oneself or to others. Or else one plunges ahead into the future, since that is the plaything of the imagination and of dreams. Often, however, the flight into the past or the escape into the future produces nothing but sadness and disgust; one finds in them a taste of bitterness and dissatisfaction.

The Noonday Devil: Acedia, the Unnamed Evil of Our Times
Jean-Charles Nault

Distraction is the corollary of instability.  No doubt you remember how Saint Thomas showed that acedia provoked a twofold movement: first a movement of flight from what causes the sadness or disgust; then a second movement of active seeking: the search for compensations, distractions.  Every man can be subject to the test of time and, therefore, to the trail of boredom; boredom that is not only a passing, external phenomenon but in the end reveals a profound incapacity of the will.  That is when someone may choose to be distracted, to “amuse oneself”, by seeking compensations or else by falling into activism.

One seeks, not fullness, but rather the accumulation of images as an evasion.  Travel agencies proliferate.  No one thinks of anything but getting away, but wherever he goes, he takes himself along.  Now if emptiness, anxiety, boredom dwell within a being, this emptiness, anxiety, and boredom will follow him to the ends of the earth.  The tenacious illusion of always being better off elsewhere does not abandon the individual.  Anything seems preferable to self-awareness and diffuse pain.
—Isabelle Prêtre, La tentation du désespoir

The Noonday Devil: Acedia, the Unnamed Evil of Our Times
Jean-Charles Nault

We can classify here also the constant tendency to consider most attractive those pursuits that take one far from home or from one’s city.  Here again we find the last daughter of acedia, instability, who thinks that by changing where one is, one can change who one is.

The Noonday Devil: Acedia, the Unnamed Evil of Our Times
Jean-Charles Nault