Seasonal Affective Disorder (SAD), according to Mayo Clinic, is a type of of depression that typically occurs each year during the fall and winter. Symptoms may include feeling tired even with plenty of sleep, feelings of loneliness and difficulty concentrating. Weight gain may also be attributed to SAD. These symptoms can vary in intensity but can be quite severe in some cases. It wasn't until the mid 1980's that the term Seasonal Affective Disorder was used by Norman Rosenthal et al. Over the past 35+ years, various treatments have been studied. Light therapy, medications and talk therapy are some of the most common treatment modalities.
It is important to talk with your primary care provider if you feel you suffer from SAD or any form of depression.