Seasonal affective disorder (SAD), also known as winter depression, winter blues, summer depression or seasonal depression, is a mood disorder subset in which people who have normal mental health throughout most of the year experience depressive symptoms at the same time each year, most commonly in the winter.

In the Diagnostic and Statistical Manual of Mental Disorders DSM-IV and DSM-5, : Although experts were initially skeptical, this condition is now recognized as a common disorder.

source: Wikipedia

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