If you were wondering, most of the explanations we get in this chapter are true. The reason that Raoden was subject to the Dor attacks was because he spent so much time practicing with the Aons. He began to make a bridge between this world and the Dor, and because of that, he gave the Dor a slight opening into his soul. I imagine that he isn't the first one to suffer something like this during the ten years that Elantris has been fallen. Other Elantrians probably practiced with the Aons, and the Dor eventually destroyed them. When it was done, they simply became Hoed.
By finally using the Dor effectively, Raoden relieved a little bit of the pressure, letting the nearby buildup of the Dor (the one that he himself had created by practicing so much) rip through him and fuel that single Aon.
Originally, I had Raoden's conflict with the Dor continue on after this scene–I had it continue attacking him. In a later draft, however, I realized that I'd made a mistake. Raoden has other things to worry about in the upcoming chapters–he doesn't need the Dor attacks to create conflict and tension. So, after this chapter, the Dor attacks actually became distractions. I also realized that the way I'd set up the magic system, this chapter was probably the place where the Dor should stop attacking, since Raoden had fulfilled what he wanted it to do.