Looking for something else, I came across some material on acedia, that spiritual state characterized by boredom, ennui, apathy, listlessness, just giving up and not caring anymore.
It’s a condition much discussed and treated in the centuries-long literature of spiritual directors, for churches that have such things–i.e., Roman Catholicism and Eastern Orthodoxy, especially in monastic circles. It’s a species of the vice of sloth. See this this article from the monastic tradition, which calls acedia “the bane of solitaries,” relates it to existential angst, and says it isn’t a sin so much, though it dangerously saps the gratitude for living and attacks the impulse of charity; that is, love of neighbor.
Acedia is said to be distinct from the psychological condition of depression. I suspect, though, that when most Christians go through this, not having access to any experienced spiritual counselors and left only with the medical profession as a resource, it’s often diagnosed as depression. Maybe some cases of what used to be called acedia really are depression. And maybe some cases of depression are really acedia. Perhaps depression is a symptom of acedia, or vice versa. (One way to distinguish the two may be the extent to which anti-depressant drugs help or don’t.)