down in the dumps, to be

To be sad or dispirited. The “dumps” referred to are not the modern rubbish heap but a heavy, oppressive mental haze or dullness (from the Dutch words domp and German dumpf). The expression was used several times by Shakespeare (Titus Andronicus 1.1; The Taming of the Shrew 2.1; Much Ado about Nothing 2.3) and was well known as “in the dumps” until the eighteenth century. See also DOWN IN THE MOUTH.