Seasonal Affective Disorder (appropriately nicknamed SAD) is a type of depression that occurs due to the changes in the seasons. SAD is most common in the cold fall and winter months but some people also suffer from summer SAD. Another names for seasonal affective disorder is: winter blues.
SAD is caused by lack of sunlight. The sun is very important because not only does it give us vitamin D but it also helps give us energy. During the cold, dark months of winter many people avoid going outside – this causes the depressive symptoms to start.