SAD or seasonal affective disorder is defined as recurring depression with seasonal onset and remission. Fall-onset (winter) SAD is more common than spring-onset SAD.
Fall-onset SAD is characterized primarily by atypical symptoms of depression, while spring-onset SAD is associated with the more typical features.
Fall-onset SAD is characterized by the following symptoms of depression:
 · Increased rather than decreased sleep (inability to get up in the morning)
· Increased rather than decreased appetite with carbohydrate craving (craving for sweet sour and salt)
· Marked increase in weight
· Irritability
· Interpersonal difficulties (especially rejection sensitivity)
· Leaden paralysis (heavy, leaden feelings in arms or legs)
The cause is imbalance of serotonin to melatonin ratio. And the treatment involves enough light exposure, artificial light exposure, sun therapy and drugs if needed.
Light therapy has proven effective. It may take 4 to 6 weeks to see a response, although some patients improve within days. Therapy is continued until sufficient daily light exposure is available through other sources, typically from springtime sun.