Seasonal Affective Disorder (SAD) is a type of depression that happens during a certain season of the year—most often fall and winter. There is no clear cause of SAD. Less sunlight and shorter days are thought to be linked to a chemical change in the brain and may be part of the cause of SAD.
Common symptoms of SAD include fatigue, even with too much sleep, and weight gain associated with overeating and carbohydrate cravings. SAD symptoms can vary from mild to severe and can include many symptoms similar to major depression, such as:
SAD may begin at any age, but it typically starts when a person is between ages 18 and 30.
On average, SAD will last about five months of the year. Typically, symptoms will develop in October, worsen around the end of daylight saving time, followed by a more drastic decline in November. January and February tend to be the months with the most severe symptoms of depression.