Jimmy is shocked at Chuck's death and believes himself to be at fault because of his interaction with the insurance company. Howard believes Chuck's death was his fault because he forced Chuck to retire. Upon hearing this, Jimmy allows Howard to shoulder the blame and regains his usual upbeat demeanor.

Why did Chuck burn himself?

Chuck began to realize that his illness was most likely psychosomatic, and the idea that his problem was all in his mind was a conclusion Chuck really didn't want to accept. ...

What caused Chuck to relapse?

In the episode, Jimmy plans to help Irene recover the trust of her friends at Sandpiper Crossing at the cost of his reputation, while Chuck is forced by Howard to resign from HHM, eventually causing a relapse of his condition.