Cyril, there is no "calming yourself". Sweaty hands are a natural indicator of light performance stress, but for people with palmar hyperhydrosis, there is no easy way to stop sweating, period.
I keep ten decks or so in rotation when I practice if my hands are sweaty. This isn't possible in an impromptu performance, when you would have no reason to have more than one deck of cards. Sweaty hands with a deck of cards for ten mins or so isn't a very bad thing for the cards. Just let them sit afterward.
A Porper is absolutely necessary - will fix a deck of cards basically overnight, even if it seems ruined by sweat. But in the long run, if you have sweaty hands, you just have to spend a lot more money on cards (in my 12 years of card experience).
Cameron