In war you do not have the luxury of having a panic attack, being anxious, angry, happy or sad. All these emotions are irrelevant to the task at hand. A momentary lapse of focus can result in death. The mission is all that matters, a singular point of focus.
The mental hardships are faced after the fact. When the battle is won or lost, only then do you have time to ruminate on the past or future. Physical combat teaches you almost the same lesson with less dire consequences. Physical combat sets the stakes. Winner takes all, the loser is eliminated.
How you feel in the fight does not matter. It is irrelevant to your opponent. Only your actions translate to reality. Any excuse or anxiety, WILL be exposed and shown via a delay in movement. A stutter. These lapses give the enemy openings.
Apply these concepts to life. Do not delay action with thought. It gives your enemy a chance, and sometimes the most fierce enemy we face, is ourselves.