Thank you all for replying =)
@TheBobs: The vomiting would work indeed, but I find it rather crude! I'm looking for a more elegant solution =)
@Eri: I am in possession of the Mistborn Adventure RPG, it just doesn't suit my (and the players') ideal of the perfect RPG. It has some nice aspects but I find the WFRP (2nd Edition ;-) ) system appliable to almost everything that requires a big sense of realism and danger. Like the world of Scadrial. The Mistborn RPG is intended to start with people who already have some power, or are even Kandra. I prefer to make an RP group of Skaa that finally get the guts (or the proper motivation *que evil laugh*) to rise up and seek the revolutionaries in Luthadel.
@Fyodor: That's a great reference, they did get sick for one day if I'm correct right? Maybe this is the direct effect of Snapping? If this is correct I can keep to my original plan in order for them to Snap, without them knowing that they have Snapped, I like it It's so much more rewarding if your players experiment on themselves because of some vague hints from my part.
@Windrunner: I'm hosting a game during the rule of the Lord Ruler, that's why I opted for getting them beaten too!