There are many symptoms of SAD. Among them are the following: Tiredness or low energy, experiencing difficulty getting along with other people, feeling hypersensitive to rejection, experiencing a heavy, « leaden » feeling in the arms or legs, frequent oversleeping, noticeable appetite changes, especially a craving for foods high in carbohydrates, which may also contribute to weight gain. There are other sypmtoms but these are the most commonly seen.
http://www.mayoclinic.org/diseases-conditions/seasonal-affective-disorder/basics/symptoms/CON-20021047