Bipolar disorder is defined by periods (episodes) of extreme mood swings that affect mood, thoughts, and behavior. 

The two main types of bipolar disorder:
- Bipolar I: characterized by severe mania (a state of very high energy that affects day to day life) and often depression
- Bipolar II:  involves a less severe form of mani known as hypomania (doesn't usually interfere with day to day life)
- cyclothymic disorder: hard to explain. see this article: 

https://www.verywellmind.com/bipolar-iii-disorder-380002

Genetics, brain abnormalities, and environmental factors are believed to be causes of bipolar disorder.

It is estimated that 4.4% of adults will have bipolar at some point in their lives.