In the Season 6 premiere episode, which airs April 7, Don goes silent in order to deal with what happens to him in Hawaii, according to spoilers from The Daily Beast.
Per the spoilers, Don undergoes a "spiritual experience" in Hawaii, which makes him go quiet for the first part of the episode.
Then, an ad campaign "becomes a jumping-off point for Don's own mental state," the article continues.
And several other characters on the show will also be facing big changes as they "look to shed their skin to remake themselves." Then again, when aren't people remaking themselves on this show on a regular basis?
Long story short: This Sunday can't come soon enough!
Source: The Daily Beast