Mopey

[T]hat is partly owing . . . to young Alexis having been desultory and mopy of late—not taking the interest in his music he did.

Source: wiktionary

He got mopy and melancholy, and couldn't or wouldn't work.

Source: wiktionary

In the 1980s, liberals nursed the fear that we really might be dwelling in an irrelevant cul-de-sac outside of the majority American culture. That kept us sullen and mopey.

Source: wiktionary