User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-122.164.246.114-20121221062619/@comment-3146930-20121222234139

That would be true if Hazel's curse was the flashbacks, but it isn't. She was having flashbacks as a result of being brought back to life in an unnatural manner, so her mind was existing in her past life and her current life, or at least that is how it is explained in the book.

Her curse is that she calls up cursed gems from the Underworld. Anyone that sells one of theses gems is cursed and normally die or are injured somehow. Because Hazel has no control over when these gems appear (as she calls them up when she is stressed), she wishes that this curse would go away.