Mood Disorders are psychiatric disorders characterized by either one or more episodes of depression or partial or full manic or hypomanic episodes. Insomnia, typically and rarely, and excessive sleepiness are features of mood disorders. Bipolar patients may show cycling between periods of depression, normal mood, mania, or hypomania. Patients with major depression only have depressive episodes and are therefore described an unipolar.

Some patients may show a seasonal pattern, with episodes frequently occurring during the winter months. This is more common in bipolar patients. Another group within the mood disorders is secondary depression, which is defined as depression occurring in connection with other psychiatric or medical disorders. The sleep findings here are usually different from those for other mood disorders. Although such mood episodes may develop within the context of a life stress, many episodes have no obvious precipitating factors.

Associated sleep disturbance is comprised of two disorders: in depression, difficulty in falling asleep; in mania, sleep-onset insomnia and short sleep duration. The most common characteristic with major depression is repeated awakenings, leading to the so-called “early morning.” Waking up early and not being able to return to sleep is the cardinal complaint. Most complain of restless sleep and tired feelings, whereas those with mania do not complain about the lack of sleep and feel refreshed.