Bipolar disorder is a brain disorder. It is also known as manic-depressive illness. It causes unusual shifts in mood, energy, and activity levels. It also affects the ability to carry out day-to-day tasks. There are four basic types of bipolar disorder. All of them involve clear changes in mood, energy, and activity levels. These moods range, from periods of extremely "up" to "down" periods. During the "up" periods one shows energized behavior. During the "down" periods he/she is very sad or hopeless. The "up" periods are known as manic episodes. The "down" periods are known as depressive episodes. Less severe manic periods are known as hypomanic episodes.

    People with bipolar disorder experience periods of extremely intense emotion. They also experience changes in sleep patterns and activity levels. They show unusual behaviors. These periods are called "mood episode”. Mood episodes are extremely different from the person’s ordinary moods and behaviors. During the mood episodes there are extreme changes in energy, activity, and sleep.

    Sometimes a mood episode includes both manic and depressive symptoms. This is called an episode with mixed features. People experiencing an episode with mixed features may feel sad, empty, or hopeless and extremely energized at the same time.

    Bipolar disorder can be present even when mood swings are less extreme. For example, some people with bipolar disorder experience hypomania. It is a less severe form of mania. During a hypomanic episode, an individual may feel very good. The person may not feel that anything is wrong. However, family and friends may recognize the mood swings. Without proper treatment, people with hypomania may develop severe mania or depression.

(Adapted from: https://www.nimh.nih.gov/health/topicsbipolar-disorder/index.shtml)

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