Seasonal Affective Disorder (SAD)

An affective disorder which is characterized by recurrent depressive episodes that occur annually at the same time each year. A subtype of major depressive disorder (MDD). Not the same as, but contains elements of depression, anhedonia, and dysthymia.

Reference:

Rosenthal, N. E., Sack, D. A., Gillin, J. C., Lewy, A. J., Goodwin, F. K., Davenport, Y., ... & Wehr, T. A. (1984). Seasonal affective disorder: A description of the syndrome and preliminary findings with light therapy. Archives of General Psychiatry, 41(1), 72-80. https://doi.org/10.1001/archpsyc.1984.01790120076010