Regret is both healthy and unhealthy. Allow me to elaborate in further detail. Initially, regret is a normal response when someone has done something they are either not proud of or when it affects or negatively impacts the lives of others, including one's own. When this occurs, it leaves a feeling of sadness, remorse and regret. This initial response is to be anticipated. Regret is an indicator that our emotions our in check. Without it, how can one gauge their words, actions and behavior? Regret is not unhealthy in this circumstance. However, in order to proceed without allowing remorse and guilt to stifle one's life, we must accept any wrongdoing, forgive ourselves, and move on.
Regret is unhealthy when we continually harbor on our mistakes, allowing it to become an obsession. It serves no good purpose to carry on excessively. Everyone makes mistakes. Everyone has experienced regret on one level or another. However, we must learn from them.
If possible, an individual can try to correct the mistake, ask forgiveness, forgive oneself, and vow not to repeat it. Our words and behavior are powerful weapons. We need to use them wisely.
Remember that we are all humans and "to be human is to err." Then move on.
Try positive affirmations, ie. I am a good person, worthy of happiness. I shall remain joyful in all circumstances. I can do better and I will. I will not allow this to disturb me anymore. I've done all I can.
All battles begin in the mind. Change your mind and you can change your life.