Hal doesn’t know it yet, but anhedonia isn’t the worst kind of depression. The worst is called clinical depression or “unipolar dysphoria.” It is an active feeling, a form of absolute torment that
Kate simply thinks of as “It.”
It is a psychic horror so painful that it is literally unbearable, and the loneliest feeling in the world. Kate suffers from psychotic depression, which is even lonelier because it involves delusion and thus isolates and disconnects her from the world.