Some people develop recurrent depression in the winter months only. This is called seasonal affective disorder (SAD). For people in the UK with SAD, symptoms of depression usually develop each year sometime between September and November. They then continue until March or April. You and your doctor may not realise for several years that you have SAD. This is because repeated depression is quite common. You may have been treated for depression several times over the years before it is realised that you have the seasonal pattern of SAD. Treatment of SAD is similar to other types of depression. However, light therapy is also effective. See separate leaflet called Seasonal Affective Disorder .