Clinical depression is one of the illnesses that cause this. A variety of other kinds of mental illness have this mindset as a symptom. Although it is not the same thing as ennui, it is another cool word that describes the human condition.

Sophisticated people in places like Scarsdale, New York have ennui and often experience anhedonia. They take Prozac and drink martinis to ward off their effects.

Folks in Jonesboro,Arkansas are bored and don't feel like doin' nothing.

They do homemade meth and run trucks into the side of houses.

What a country!

Anhedonia trivia:

This was the working title of Woody Allen's movie Annie Hall. He was told to drop it because nobody would know what it meant.