Per Rabbi Shimon Eider's Sefer Hilchos Nidah one should "refrain from listening to his wife's singing when she is a Niddah."

Should a woman avoid singing in front of her husband while she is a niddah?

  A boy is highly confident one day and
  the next day scared, timid and shy. 
  
  A girl is emotional one day and
  emotionless the next.


Is there a term for a drastic switching of emotions?
A term for the switching to practically opposite emotions?

EDIT: Just to clarify the emotional changes are not rapid, and are permanent.  This rules out bi-polar, because bi-polar involves multiple periods of change.

EDIT2: I'm looking for a work to demonstrate the steepness or contrasts of change, but having no relationship to the speed of change.

Example:


  Over a course of 3 years a once quiet boy become the spokesmen of the school.

