In One Flew Over the Cuckoo's Nest by Ken Kesey, how does Chief Bromden's experience with "the fog" change after the fishing trip?

Returning from the fishing trip, Chief Bromden experiences increased clarity of mind and a strengthened sense of agency. After McMurphy and Bromden are taken to the Disturbed ward, Bromden describes the effects of ECT (electroconvulsive therapy):

There had been times when I’d wandered around in a daze for as long as two weeks after a shock treatment, living in that foggy, jumbled blur which is a whole lot like the ragged edge of sleep, that gray zone between light and dark, or between sleeping and waking or living and dying, where you know you’re not unconscious any more but don’t know yet what day it is or who you are or what’s the use of coming back at all—for two weeks. If you don’t have a reason to wake up you can loaf around in that gray zone for a long, fuzzy time, or if you want to bad enough I found you can come fighting right out of it. This time I came fighting out of it in less than a day, less time than ever. And when the fog was finally swept from my head it seemed like I’d just come up after a long, deep dive, breaking the surface after being under water a hundred years. It was the last treatment they gave me (Kesey 160).

In the above passage, Bromden notes the rapidity with which he recovers from the fog and compares it to earlier experiences lasting upward of two weeks. The language used is particularly important because Bromden describes his recovery as "fighting," and in his word choice we can interpret sensations of inner strength, resilience, power, and agency: key concepts for Bromden, who, as a mentally-ill minority figure, has suffered from significantly reduced agency within the novel. Furthermore, we see that the act of coming out of the fog is purposeful; that is, whereas Bromden's earlier experiences in the fog left him wondering "what [was] the use of coming back," he implies that there is a reason or drive to do so after the fishing trip. It is also worth noting that this is the last treatment Bromden receives in the novel as he leaves the ward by its conclusion, but significantly, this particular experience leaves him feeling as though the fog, which has clouded his thoughts and perceptions for a prolonged period, has lifted in such a way that suggests it will not return. 

Because the fog has lifted for Bromden, it also allows him to contemplate thoughts such as the following:

We had just unlocked a window and let it in like you let in the fresh air. Maybe the Combine wasn’t all-powerful. What was to stop us from doing it again, now that we saw we could? Or keep us from doing other things we wanted? (Kesey 168)

The fishing trip reinforces an attitude that develops in Bromden and the other ward patients throughout the course of the novel: the patients do have the power to dictate the course of their lives and to exist in the outside world. In the passage above, Bromden challenges the authority of the Combine, an entity he has feared throughout most of One Flew Over the Cuckoo's Nest. For Bromden, the dissipation of the fog signals the dismantling of the Combine's power.

(Source: Kesey, Ken. One Flew Over the Cuckoo’s Nest. New York: Signet Books, 1962.)