The Faery Sickness came about when I read an article about a small village that still believed in the fae. They didn't have modern medical exposure or help and so, when babies died, they were said to have been "taken by the faeries". When medicine did arrive in their village, and the babies stopped dying, they were asked what they thought. Their response was that the faeries weren't taking so many babies now. They didn't really associate the fact that medicine had played a big role, just that the fae were appeased somehow. So, I started thinking, what if the fae really were taking the babies, and what if someone tried to defy them and find out exactly why. And Vala was the perfect person to do that.