Seasonal affective disorder (SAD): Seasonal affective disorder (SAD), a form of depression that tends to occur as the days grow shorter in the fall and winter. It is believed that affected persons react adversely to the decreasing amount of light and the colder temperature as autumn and winter progress.
The symptoms of SAD include regularly occurring symptoms of depression (excessive eating and sleeping, weight gain) during the fall or winter months and full remission from depression in the spring and summer months, with no nonseasonal depressive episodes. A craving for sugary and/or starchy foods has also been said to be characteristic of SAD and separate it from other depressive disorders.
Seasonal affective disorder has not been recognized very long as a medical condition. The term first appeared in print in 1985. Seasonal affective disorder is also sometimes called winter depression or the hibernation reaction.