Bipolar disorder is a mental illness characterized by periods of mania and depression.  It was previously known as manic depression.

Periods of mania consist of a feeling of euphoria, restlessness, energetic, talkative. During this time, individuals with bipolar disorder may participate in risky behaviors. Mania can also include anger, irritability and confusion. During the mania stage, individuals may sleep for only short periods of time.

Depression includes symptoms of sadness, feelings of worthlessness or helplessness, loss of energy, loss of pleasure.

In between mood swings, people with bipolar often experience moods consistent with a person without bipolar disorder.

For more information:

Bipolar and ADHD