Bipolar disorder is an illness where the person's state of mind alternates between extremes.
Periods of desolation, causing lethargy alternate with bouts of mania characterised by excessive excitement and activity. These are often separated by periods of normal mood. Bipolar disorder is characterised by extreme states of mind, from depression through to mania. A particular state of mind can last many months but the mood will fluctuate. Men and women are equally likely to get bipolar disorder.