SAD (Seasonal Affective Disorder) Many people eat and sleep slightly more in winter and dislike the dark mornings and short days. This is known as 'winter blues'. Others have more severe symptoms which such as sleep problems, withdrawal, overeating, depression, anxiety and lethargy. These often lead to difficulties at home, work and in relationships. This is a recognised problem known as Seasonal Affective Disorder (SAD). SAD is caused by the lack of bright light in winter. Light entering our eyes stimulates our brain to control our daily rhythms through hormone production. In some people, the low levels of light in winter are insufficient to regulate the hormones that affect our waking up and sleeping, our feeling energised or depressed.