There was a police officer in my city who was seriously wounded several years ago when a guy pulled a gun and shot him during a traffic stop. He was on the ground, gut shot, and managed to pull his gun, shoot and kill the perp. He said that during the whole incident, everything was moving in slow motion and he could hear his range instructor in his head saying, “SQUEEZE the trigger! SQUEEZE the trigger!”
In the old revolver days when you went to the range you would simply put your empty brass into your pocket so you wouldn’t have to pick it up when you were finished. What do you do under stress? Revert back to your training, just like you said. They stopped that practice when they found a dead state trooper with his hand in his pocket full of spent brass after a shoot out.