I think I may have seasonal affective disorder. What is SAD and what can I do about it?

Seasonal affective disorder (SAD), also known as winter depression, is a problem all too familiar to New Englanders and others who live in northern latitudes. SAD is “not just feeling bummed out because it’s winter,” said Janis Anderson, director of the seasonal affective disorder service at Brigham and Women’s Hospital. It includes physical changes such as trouble getting up in the morning, lack of energy, gaining weight and problems concentrating, for weeks or months at a time. Symptoms typically start in the fall and lift in the spring.