Pretty much everything has been said that needs be said on this, but I'm always happy to give my own little twist on things.

Zymosis was a very interesting event, but again, I had it from the Dawn/Order side of things. Since it wasn't clear how the disease was created, Mae and other dragons at the time theorized that it was an mutation of the Biped Disease (then after called Duskael Morbidae), which was 'responsible' for turning dragons into bipeds before the RoP was finished. This terrible disease worked in three stages: the first, the dragon would laze about and it was initially hard to tell something was wrong; the second, the dragon would not move at all and slowly the scales would brown and fall out; and last, a newly formed biped would crack free from the shell the dragon once was, doomed to slowly forget about the life it once led as a dragon.

Mae loves to tell that story to hatchlings. ;p

Thankfully, it is believed that dragons are now immune to that disease... or so it is hoped.