A bipolar disorder is a psychiatric condition that is characterized by alternating cycles of changes in mood. These mood changes can be severe, the mood may shift from an extreme high (manic) to an extreme low (depression).
Manic behavior is due to an abnormally elevated mood and may include inappropiate elation, severe insomnia, and increased irritability. Poor social judgment is common. All behaviors are amplified in mania. For example, if the person drinks, they will drink way too much. If the person goes shopping, they will spend way too much and often will write bad checks for the purchases. The person knows they don't have the funds to cover the purchases but they do it anyway.
Depression is hallmarked by periods of extreme sadness, the loss of interest in normal activities, and thoughts of despair and worthlessness.
The mood may change from day to day or the person may be depressed for a couple of days then revert back to manic behavior and stay in a manic state for several days.
Bipolar disorder is a condition in which people experience abnormally elevated (manic or hypomanic) and, in many cases, abnormally depressed states for periods of time in a way that interferes with functioning. Bipolar disorder has been estimated to afflict more than 5 million Americans—about 1 out of every 45 adults. It is equally prevalent in men and women and is found across all cultures and ethnic groups. Not everyone's symptoms are the same, and there is no simple physiological test to confirm the disorder. Bipolar disorder can appear to be unipolar depression. Diagnosing bipolar disorder is often difficult, even for mental health professionals. What distinguishes bipolar disorder from unipolar depression is that the affected person experiences states of mania and depression. Often bipolar is inconsistent among patients because some people feel depressed more often than not and experience little mania whereas others experience predominantly manic symptoms. (wikipedia)