A category of mental illnesses in which mood and affect are disturbed—characterized by irregular cycles of mania and/or depression. During manic periods, the individual may be in a very elevated mood and exhibit symptoms of hyperactivity, wakefulness, and distractibility or irritability. In very severe episodes, psychotic symptoms may also be present. Individuals experiencing depressive periods can exhibit sustained symptoms of depressed mood, diminished pleasure or interest in most activities, fatigue, sleep disturbance (either insomnia or hypersomnia), weight loss or weight gain, and slowed thinking.
Source: Children Welfare Information Gateway