This Sunday, millions turn their clocks back one hour as we “fall back” into winter. While the extra hour of sleep is enjoyable, for many, the decreased sunlight is not.

Seasonal Affective Disorder (SAD) is a type of depression that occurs during certain seasons, typically winter. While the exact cause is unknown, some believe it is related to a disruption in our circadian rhythm due to decreased hours of sunlight.

For many, SAD starts this time of year, when we “fall back” and “lose” an hour of sleep and sunlight.

“About 6-percent of the U.S. population is diagnosed each year,” says Dr. Lynnae Hamilton with Adventist Healthcare Behavioral Health and Wellness Services. “You can have this type of disturbance that will start in the fall or winter and it can hang on with you until spring.”

While Dr. Hamilton says that SAD is more likely in younger people, she also notes that you cannot outgrow the disorder and it can occur in anyone.

Symptoms of SAD include irritable feelings, loss of interest, weight gain and trouble concentrating.

Clinician often treat SAD using light therapy to “reset” the circadian rhythm. If you think you or a loved one may have SAD, speak with your doctor.

For more information about SAD and its impact this time of year, read Dr. Hamilton’s interview with CBS news earlier this week.