The more intense and stressful the situation gets, the calmer you must become. This is the law.
I understand that this isn’t a natural reaction for most people – but that doesn’t mean that they can’t do it.
This is one of those cases where the old adage “fake it ‘till you make it” really works. Unless you are a psychopath (in which case you don’t break a sweat in a crisis naturally), you just have to force yourself to remain calm until it becomes second nature. If you can do it, you get the nice bonus of an adrenaline rush.
Like getting good at most things, it’s really just a question of practice. The problem is, most people don’t get exposed to chaotic crises very often.
A bit of a “catch 22,” but there you go.