<unk>  mood variations are believed to be related to light. An argument for this view is the<unk> ness of bright-light therapy.<unk>  is measurably present at latitudes in the Arctic region, such as northern Finland (64°00′N), where the rate of<unk>  is 9.5%. Cloud cover may contribute to the negative effects of<unk> . There is evidence that many patients with<unk>  have a delay in their circadian rhythm, and that bright light treatment corrects these delays which may be responsible for the improvement in patients. The symptoms of it mimic those of dysthymia or even major depressive<unk> . There is also potential risk of suicide in some patients experiencing<unk> . One study reports 6–35% of sufferers required hospitalization during one period of illness. At times, patients may not feel depressed, but rather lack energy to perform everyday activities. Subsyndromal<unk>  is a milder form of<unk>  experienced by an estimated 14.3% (vs. 6.1%<unk>  of the U.S. population. The blue feeling experienced by both<unk>  and SSAD sufferers can usually be dampened or extinguished by exercise and increased outdoor activity, particularly on sunny days, resulting in increased solar exposure. Connections between human mood, as well as energy levels, and the seasons are well documented, even in healthy individuals.
Seasonal affective disorder
Major depressive episode
Major depressive disorder
Depression 
Late life depression
Premenstrual syndrome
Secondary mania
Postpartum depression