Although some people can begin to feel quite good upon starting to forgive another, these positive feelings can take time because the process of forgiving itself can take time. So, it is typical that a decision to forgive can and does open the door to feeling well, but we then need patience to keep on the path of forgiveness. As we do that, anger begins to diminish and feelings of well-being begin to emerge. Even if the anger does not go away entirely, many people then say that their anger no longer controls them.
Can people feel well if they do not forgive? This depends on the severity of the offense. If the offense is profound and shocking, then a person may not feel well in a general and on-going sense without forgiveness. I do not say that to put pressure on anyone to forgive. I say it, instead, because this is what I observe in those with extremely challenging injustices against them.