And a very condensed note I wrote to myself (in brainstormish mode, without regard for feasibility or testability):

Emotions are filters on the brain, brain subsystems activated for different reasons in response to different cognitive stimuli. This would explain why those who are happy have a hard time remembering things that are saddening or vice versa (possibly causing cascades). It seems that flow is the opposite of suffering, as both are responses to difficult problems such as the ones the brain evolved to solve. Pain asymbolia may be the opposite of something like bipolar disorder or multiple personality disorder, and the difference may be strength of emotion or the cognitive subsystems similar to emotion. It is odd that people who suffer are more often negative utilitarians: this is probably because the suffering filter is affecting what sorts of memories of experience they have access to, and biasing their thoughts in that direction.