Bipolar Disorder is comprised of various types, the most severe of which is Bipolar I Disorder. Also known as "manic-depressive disorder," Bipolar I is characterized by dramatic mood swings between "poles" of mania and depression, which can adversely affect a person's normal daily activities, damage relationships, and result in poor performance at work or school. Bipolar I Disorder's "manic" phase may encompass sudden euphoria or rage, along with hyperactivity, garrulousness, decreased need for sleep and reckless behavior. Inflated self-esteem, racing thoughts, preoccupation with irrelevant or unimportant matters, extravagant shopping sprees, risky sexual behavior, or foolish investments are also characteristic. In contrast, the "depressed" phase of Bipolar I Disorder mirrors the symptoms of Major Depression: persistent fatigue and sadness; lack of interest in activities once enjoyed; changes in sleeping and eating patterns; difficulty concentrating; feelings of hopelessness and worthlessness; and thoughts of death or suicide. The mood swings of Bipolar I Disorder are called "episodes." Sufferers may experience both manic and depressive episodes, as well as episodes of "hypomania," a milder form of mania characterized by hyperactivity and euphoria. Episodes of mania typically begin suddenly, and last an average of four months. Depressive episodes may last longer, persisting for approximately six months, but rarely longer than a year. In some instances, symptoms may be so severe that hospitalization is required, either in the case of severe depression where the person is at high risk for suicide, or because a person experiencing a manic episode is completely out of control. Bipolar I Disorder sufferers may also experience "mixed" episodes, which are characterized by depression, along with symptoms of mania or hypomania including anxiety, irritability, racing thoughts, insomnia and agitation. It's believed this combination of manic and depressive symptoms may significantly increase the risk of suicide. While the precise cause of Bipolar I Disorder is not known, experts believe that a number of factors-including biological, genetic and environmental components-may be responsible. Research suggests those with Bipolar I Disorder may have imbalances in important brain chemicals called neurotransmitters, such as norepinephrine, serotonin and dopamine, each of which plays a role in mood and emotions. In addition, about half of sufferers have a family member with a mood disorder. Having a parent with Bipolar I Disorder may pose a 15-25% risk of developing the illness; an identical twin with the disorder may increase risk to more than 85 percent. Bipolar I Disorder may also commonly occur in conjunction with alcoholism or drug addiction, as well as with other mental disorders such as Anorexia, Bulimia, Attention-Deficit Hyperactivity Disorder, Social Phobia and Panic Disorder. Studies suggest Bipolar I Disorder is equally common in men and women, and most often develops in the late teens or early adulthood, but may occur in children as young as preschool age. According to the American Psychiatric Association, diagnosis of Bipolar I Disorder involves at least one manic or mixed episode, and may involve at least one episode of depression. With proper diagnosis and treatment, most people with Bipolar I Disorder can lead healthy and productive lives. If you think you may be suffering from Bipolar I Disorder, please see a mental health professional.