down in the dumps

Example: “She's been down in the dumps since her best friend moved away.”

Origin: "Dumps" for a state of gloom or melancholy is English by the early 1500s, most likely from Dutch domp (mental haze, dullness) or German dumpf (heavy, oppressive, gloomy) — either way, a word for mental heaviness well before it paired with "down." Shakespeare used "dumps" this way across four plays and in his poem The Rape of Lucrece, so the word alone was thoroughly established by his time. The specific phrase "down in the dumps" is first recorded later, in Francis Grose's 1785 Classical Dictionary of the Vulgar Tongue. A tongue-in-cheek rival story blames an Egyptian king named Dumpos who supposedly died of melancholy, but this is a widely acknowledged invented etymology rather than the real source.