Answer:
Bipolar disorder.
Step-by-step explanation:
After being depressed for about six months, Lewis starts talking so rapidly and so excitedly to his neighbors about his new idea that they can hardly understand him. Lewis most likely suffers from bipolar disorder. Manic-depressive illness or bipolar disorder causes unusual and clear shifts in mood, energy levels, and activity levels. As happened with Lewis, after a depressed mood he shifts to excited mood and big energy and activity levels.