Seasonal Affective Disorder, or SAD is a mood change that occurs when days get shorter and less sunlight is available. It usually starts in fall or winter and improves when spring returns.
Sometimes called the "winter blues," SAD is not a disorder on its own but is classified as a type of recurrent depression. According to the National Alliance on Mental Illness, persons with SAD tend to crave carbohydrates, and they eat too much. They may withdraw from social situations and self-isolate with a feeling they need to "hibernate" until the sun returns.
Almost everyone with SAD sleeps more than they need to. They may lose interest in formerly enjoyed activities and have difficulty concentrating. SAD can make a person gain weight, feel agitated, and show other signs of major depression, as well.