Loneliness.

The word and concept arrived in English
with the Industrial Revolution.
The word solitude remained, with its original,~
neutral meaning.

But the Greeks knew all about loneliness.
For them, it was a state of isolation,
outside the polis or commune,
in the bleak érema (back of beyond, the boondocks,
the sticks, the wolf-haunted wildness or wilderness
beyond the pale of masters and slaves).

An éremos was a solitary, maybe abandoned,
maybe lonely person, absent from civilisation,
lacking in amenities, possibly  one of thousands
of children abandoned 'abroad' and brought up by wolves.
On the other hand, an éremitos was solitary by choice
in a 'lonely, deserted' place teeming with flora and fauna -
hence our word hermit.  The Irish word for a hermitage
was díseart (anglicised dysart) from Latin diserta, a place without people.

Some Irish hermits lived on islands and islets
from birds' eggs, seaweed, sea-scurvy-grass, mussels and limpets
- and may not have wanted for company.

Listen on my website to a brief discussion on the BBC
of contemporary loneliness.

Loneliness goes - and is often confused with - Boredom.
But you're never alone while you still have thoughts.
Even hatred can be pleasant company.

Here is an excellent Aeon article discussing Hannah Arendt's views on loneliness.
However, what Arendt ascribed to Totalitarianism is equally a result of Consumer Capitalism.

https://aeon.co/essays/for-hannah-arendt-totalitarianism-is-rooted-in-loneliness