...there is one thing you can do that has helped many warriors to make the dreams go away: train. The puppy is worried, so to calm him you teach him a few new tricks or polish the old ones. Train hard so that he feels confident.
I know an officer who is a member of one of our nation's most elite SWAT teams. He goes into harm's way on a daily basis and is confronted by deadly force encounters on a weekly basis. He tells me that every six weeks, like clockwork, his nightmares return. To make them go away, he goes out to the firing range on a Saturday and fires hundreds of rounds. He particularly likes to shoot at steel targets, the kind that produce an audible clank when struck and then drop down. "My weapon turns into a magic wand. Wherever I point it, things fall down, and my nightmares go away."
For some people, the nightmares pass when they are no longer in danger. Others seem to "learn" how to win in their dreams, to "will" themselves to win, even if it means picking up a big rock and smacking their enemy with it, or defeating an endless stream of attackers until their opponents finally give up. However, if the nature of your work is that every day you face combat or the possibility of combat, one possible solution is to train.
The midbrain or the mammalian brain truly is like having a "puppy" inside. The only way to communicate to your puppy is to train him. I have two dogs, a poodle and a German shepherd: my elite, crack security team. I cannot talk to my dogs, and tell them, "All right, I'm going to be gone for a week, so you guys are in charge. You've got the front door, and you've got the back door." It's not like Scooby Doo where they say, "Rr-all right boss!" and go do it. In the real world the only way you can communicate to your dog is to train him. The same is true with the puppy inside.
The one quality all good police dogs have in common is confidence, verging on cockiness. This is because they have been highly trained and they know that there is nothing the world can throw at them that they cannot handle. Have you ever seen a person that just exudes confidence under stress? You can't fake it, it is a product of training and experience. If you are having performance anxiety dreams, it may mean that the puppy doesn't have that confidence. The only sure way to get it is through training.
From On Combat, The Psychology and Physiology of Deadly Conflict in War and in Peace (p. 157)