The factors and variables affecting pain perception are not clear. Studies trying to match predisposing factors with pain and outcomes are ongoing. It's a little like the chicken and the egg question. Which came first: the pain and then the response to it? Or does the difficult personality predispose the individual to higher pain intensities?
We just don't know yet. Perceived unpleasantness and a generally negative outlook on life do seem to go hand-in-hand with increased perceptions of pain. But some early studies looking at the natural chemicals released by the body in response to pain suggest a different explanation.
It's possible that people who express anger more easily than others are slower to release these natural pain killers. They may have a higher threshold for triggering the release of the body's natural opioids. They may not have a deficient opioid analgesic system after all.
According to at least one study, anger management style has more to do with it than just general negative affect. Affect refers to our outlook and approach to things. It turns out that people who are more likely to hold anger in and not express it, have a higher release of the natural body chemicals against pain.
The opposite is also true. People quicker and better able to express anger have lower levels of the natural opioids to fight against pain. Finding ways to trigger the release of natural opioids is the focus of future studies.