|| Seasonal affective disorder (SAD), also known as winter depression or winter blues, is a mood disorder in which people who have normal mental health throughout most of the year experience depressive symptoms in the winter or, less frequently, in the summer, repeatedly, year after year. The US National Library of Medicine notes that "some people experience a serious mood change when the seasons change. They may sleep too much, have little energy, and crave sweets and starchy foods. They may also feel depressed. Though symptoms can be severe, they usually clear up." The condition in the summer is often referred to as Reverse Seasonal Affective Disorder, and can also include heightened anxiety.
There are many different treatments for classic (winter-based) seasonal affective disorder, including light therapies with bright lights, anti-depression medication, ionized-air administration, cognitive-behavioral therapy, and carefully timed supplementation of the hormone melatonin.