Answer: Bipolar disorder (Maniac-Depressive disorder)
Explanation: Bipolar disorder is a mood disorder that causes the person to experience the two sides of the emotional spectrum (being depression and mania). Bipolar patients are extremely fragile and any stressor can potentialy change their mood.
They have depressed periods where they feel inferior, worthless and don't want to do anything but they also have mania periods where they feel extremely agitated, happy and sometimes delusional.