Seasonal Affective Disorder (SAD): Symptoms, Causes, and Treatment Options As the days grow shorter and temperatures drop, it’s common for energy and mood to shift. For some people, however, these changes go beyond the winter blues. This may be Seasonal Affective Disorder (SAD), also known as seasonal depression. SAD is a type of depression that follows a seasonal pattern, most often starting with the fall and winter. The good news is that SAD is very treatable, and many people feel better with the righ...