The darkness of winter really does affect some people's moods. Sadness, anxiousness, loss of interest in activities, or sleeping more every winter can be a sign of depression called seasonal affective disorder (SAD). An estimated 10% - 20% of people in the U.S. experience a mild form of winter onset SAD, and it seems to be more common in women.
Coping tip: If you have symptoms, see your doctor. Treatment is available.