Seasons are changing. As the weather gets closer to autumn and winter, the days are becoming shorter. Accordingly, the amount of sunlight one can receive within a day became noticeably shorter. Sunlight plays a vital role in regulating biological processes for all living organisms. It stimulates the production of serotonin and increases melatonin levels, both of which are essential neurotransmitters for the human body. A deficiency in serotonin can lead to depression, while an excess of melatonin can cause drowsiness and lethargy, disrupting the body's internal clock. These changes may contribute to the onset of Seasonal Affective Disorder (SAD). Seasonal Affective Disorder is a type of depression characterized by a feeling of melancholy during specific seasons. Typically, people with Seasonal Affective Disorder experience symptoms from autumn to winter. However, some exceptions exist, with some experiencing SAD during the spring and summer. The symptoms of SAD are similar to those of Major Depressive Disorder: one might feel depressed, tired, unmotivated, worthless, and have difficulty concentrating. People with SAD, especially during winter, often feel more exhausted, sleep longer, and crave carbohydrates, which can lead to weight gain. One of the most effective treatments for SAD is spending time in sunlight. This helps regulate the body's internal clock and balances neurotransmitters, addressing the casual depression that anyone can experience at some point of their life. It is important to monitor his or her changing moods with a better understanding of biorhythms, especially in preparation for SAD.