acedia

Perhaps the best term for Fran’s persistent mood is acedia, that feeling of not caring much about anything, especially one’s position in the world.

In the early medieval era, Christian monks were very concerned about acedia.

I think acedia is still with us, but it emerged at this time when the culture needed a term to describe a specific experience.

"Sloth" is apparently a mistranslation: "When you read these descriptions of acedia, it's patently clear that what these early Christian writers are writing about, it's boredom. The things they have around them are deprived of all life, of all substance. They find nothing in them."

The literal meaning of acedia, derived from Greek, is something like "not caring," which explains why "boring" is subjective.