Some researchers believe that melatonin may play a similar role in how season effects mood of patients with seasonal affective disorder. Seasonal affective disorder (SAD) or mood disorder with seasonal pattern is a condition where the normal biorhythm is disturbed during a season, especially autumn-winter. Patients may begin experiencing or experience worsening of depressive symptoms. Patients complain of being constantly tired, craving sugary foods, overeating, and over sleeping.