Seasonal Affective Disorder (SAD)
An affective disorder which is characterized by recurrent depressive episodes that occur annually at the same time each year.
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. doi: 10.1001/archpsyc.1984.01790120076010.