Amy Lee has such a great voice. You can hear her grief in the lyrics, in her voice and it gives the song power. It' a song that moves everyone really.
Her sister died at age 3 from an (unknown?) illness when Amy Lee was six, I think. That's where the line 'Has no one told you she's not breathing? ' comes in. From the lyrics, it seems that she forces herself to believe that it's all a dream but something then makes her realise that it's real but her sister is there, always, reminding her of yesterday.
At least, that's my opinion.