I can't find the reference to the post by Larian, but they already explained it.
Talana is real and she bequeath her powers to her arch nemesis. She also gives you the vision priot to her death. One you wake up, Talana is dead and Ygerna is in your head. Since you have not undergone the mind ritual you are vulnerable to suggestion. This is what gives Ygerna the opportunity to impersonate Talana after her death.
Last edited by candlebbq; 14/12/10 08:49 AM.