I have carried for years, and have often said that I fully expect that my extensive training and practice would kick in and I would do whatever is necessary to stop a deadly threat.
OTOH, I have also said that, afterward, I fully expect that I would be traumatized at having been forced to inflict deadly harm on another person -- and I wonder if I could handle the remorse of having had to use my weapon on a young person.
But -- defense comes first; remorse comes later...
You must live through the event to be able to live through the anguish, should it ever come to that. A doctor may be able to help any problems I have with having to use deadly force after the fact. But they certainly won't be able to bring me back from the dead.