Seasonal affective disorder, or SAD, is a form of depression related to the seasons, very often winter when sunlight is at a minimum. Though many of its symptoms -- sadness, fatigue and changes in weight or sleep patterns -- are similar to those of depression, SAD symptoms tend to appear as the seasons change. As many as 6 percent of people in the United States have this type of seasonal depression, with about 10 to 20 percent more experiencing a less severe form, known as the winter blues. But there's a ray of hope for people with SAD: steps to help prevent it and ways to treat SAD symptoms.
QUIZ: How Much Do You Know About Seasonal Affective Disorder?