Flipping the Whale (2001)

Captain William Moore leads an expedition of scientists into the "Ravenswood Ocean", a dimensional realm where dreams and memories of the human race collect. The goal is to study the Ravenswood in an effort to guide humanity toward more effective inner harmony, but it eventually becomes clear to the other scientists that Moore has only been using the expedition to reunite with his dead ladylove, Amy. For a time, they take control of the mission away from him...but when they find that their efforts only cause trouble with Jeffrey, the resident demon of the Ravenswood, they turn command back over to William Moore. Moore convinces the other scientists to leave him alone in the Ravenswood to deal with Jeffrey in his own way. When the scientists return to the Ravenswood two years later, they're eager to witness the methods Captain Moore has employed, which have apparently caused a notable upward shift in the mental well being of the human race...only to find that he's been reduced to a complete degenerate, wallowing around in the haunting leftovers of his life's tragedies.