Seasonal Affective Disorder (SAD) is a type of depression that is related to changes in seasons. It typically affects individuals during the fall and winter months, when there is less natural sunlight. Symptoms of SAD can include feelings of sadness or hopelessness, low energy, difficulty sleeping, changes in appetite or weight, and difficulty concentrating. SAD is thought to be related to changes in the body’s internal clock, as well as a decrease in serotonin and melatonin levels due to reduced exposure to sunlight.