Experiencing sadness, melancholy, or mild depression; having low spirits.
The association between blue and sadness has complex origins, possibly from the 'blue devils' (hallucinations from alcohol withdrawal) or from the practice of flying blue flags on ships that had lost officers. The phrase gained popularity through blues music in the early 20th century, where 'having the blues' became synonymous with melancholic feelings.
Curiously, the blue-sadness connection isn't universal across cultures - in some societies, blue represents peace or spirituality. The phrase might also connect to the physical appearance of someone who's cold or oxygen-deprived, both of which can accompany depression's physical symptoms like poor circulation and shallow breathing.
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