I agree with Nanci about overheating probably being the culprit. Hatchlings are notorious for being lousy at regulating their core temps. Environmental factors, as suggested by Dave, should never be ruled out as possible factors.
And here's the Golden Rule of all Living Beings, "Sh@t Happens!" You don't have control once the animal leaves your possession either. And it ceases to surprise me what information people withhold when claiming illness in an animal they purchased. I've come to believe TV's Dr. House in the fact that all patients lie or fail to give all the necessary information. Sometimes it is out of ignorance but not always.
This could easily be a preexisting condition that only came to light once the animal reached a given stage of development. Many animals do well for the months and then die for no known reason during Feb. and March which would be the normal time for their wild brethren to come out of Brumation. Who knows what ticking time bombs (cerebral aneurysms, aortic malformation, intestinal strictures, etc,) any living creature might be carrying around?
It's a bummer but no doubt part of life.
Terri