Seasonal affective disorder (SAD) is a type of depression that occurs at specific times of the year, most commonly during the winter months when daylight hours are shorter. Symptoms may include feelings of sadness, fatigue, and changes in sleep or appetite. The lack of sunlight is believed to disrupt the body's internal clock and affect levels of serotonin, a neurotransmitter linked to mood regulation. Treatment options for SAD often include light therapy, which involves exposure to bright artificial light that mimics natural sunlight. Other approaches may include psychotherapy, medication, and lifestyle changes, such as increased outdoor activity and exercise, to help manage symptoms.