50 Plus.com tells us:

Last month, Margaret Trudeau (ex-wife of former Canadian Prime Minister, Pierre Elliot Trudeau) made headlines once again when she revealed that she suffers from bipolar disorder - a disease which she believes began after a post-partum depression following the birth of her second son Alexandre in 1973, but which was only recently diagnosed.

What is bipolar disorder? Wikipedia explains it this way:

Bipolar disorder, also known as manic-depression, is a psychiatric diagnosis referring to a mental health condition defined by periods of extreme, often inappropriate, and sometimes unpredictable mood states.

There are several different types of bipolar disorder. From Web MD:

• Bipolar I disorder involves episodes of severe mood swings, from mania and depression.
  
  
• Bipolar II disorder is a milder form, involving milder episodes of hypomania that alternate with depression.
  
  
• Cyclothymic disorder describes even milder mood changes.

Bipolar disorder affects between tow and three million people in America.