Millions suffer severe depression in winter Symptoms usually begin between September and November and do not lift until the Spring. Seasonal affective disorder is more than feeling a little low because the clocks have gone back, with signs including negative thoughts, despair, apathy, sleeping more, fatigue, over-eating and difficulty concentrating. It can begin at any age but most often occurs between the ages of 18 and 30 and can strike throughout the northern and southern hemispheres but is rare in people living near the Equator. SAD is thought to be caused by a chemical imblanace in the brain caused by the shortened days and lack of sunlight. Some people only suffer mildly but for others it can debilitating meaning they cannot function normally without medication. For more than eight out of ten sufferers symptoms improve with the use of a lightbox, emitting extremely bright light for up to four hours a day. Anti-depressants are rarely effective but talking therapies may help sufferers to accept the condition.