Unfortunately, in a combat situation this is usually revised to read:
If you can keep your head when all about you
Are losing theirs and blaming it on you;
you probably have no idea how many guns are currently aimed at you.
In Band of Brothers, a solder suffered from hysterical blindness and was stuggling very much with it - dying. One soldier finally told him how HE dealt with the possibility of death. The solder said “When you admit you are already dead, it becomes much easier to cope.”
:)
:)