I am by no means a Gaiman fan, but I read his Sandman and heard him speak at MIT. He mentioned that he knows how the Endless family member Delight became Delirium but wouldn't reveal it to anyone. With everything that's come out, I have a new theory that his stand-in character Dream is to blame for her condition. Here's Delirium's first appearance in Sandman #21, written by Gaiman with pencils by Mike Dringenberg and inks by Malcolm Jones III.
