noun
seasonal depression; seasonal affective disorder
Medical/psychological term for depression that occurs at certain times of the year, typically winter. Often used synonymously with 季節性感情障害 (SAD).
See also: 季節性感情障害
冬になると気分が落ち込むのは、季節性うつ病の可能性がある。
If you feel down when winter comes, it could be seasonal depression.
彼女は季節性うつ病と診断され、光療法を始めた。
She was diagnosed with seasonal affective disorder and started light therapy.
Compound of 季節性 (seasonal) + うつ病 (depression). A modern medical term, likely a calque from English 'seasonal depression' or 'seasonal affective disorder'.