Although reports says that SAD is a depressive disorder that often affects people during seasonal change, it's different than winter blues or major depression.

Allure explains, "For most people with SAD, depression symptoms start in late fall or early winter and dissipate by spring and summer."

Symptoms of SAD include mood changes like hopelessness, changes in appetite and energy levels, and in severe cases, suicidal thoughts.

"Patients with SAD tend to develop a lethargic depression as opposed to more irritability — think being glued to the couch rather than lashing out at a loved one."

Experts say that SAD could be caused by serotonin imbalances, a chemical in the brain that contributes to a positive mood. If you or someone you know is experiencing depression, whether seasonal or not, experts say to visit a doctor.