But why do they hurt?
In her golden omniscience, she saw it all. She saw her precious Doctor changing, a new man with a new face, and she saw his love for her. With a flash, she was on the beach sobbing as he faded away.
Another flash, and he left her again on the same beach; she saw him losing his new companion, the Doctor Donna, and then losing all reason and dying once more.
Flashes of friends dying, Sarah Jane, fierce to the last but killed by a wasting disease, Mickey and Martha Smith on another planet overwhelmed by hostile forces, Donna Noble who never remembered.
I can see everything... all that is... all that was... all that ever could be.
Flashes of people she didn't know and would never know, nightmares of galaxies colliding and stars burning out, and a man falling from the stars, a broken god fallen to earth. And she saw a new love. A painful love, a broken love, but even brokeness can be beautiful, like a fractured glass, all rainbows and sharp edges.
Rose gasped.
This was too much too soon, she couldn't lose him, her Doctor, she couldn't see the future and past and end of things at the same time all the time pouring through her head, she couldn't be the Bad Wolf.
As the Doctor kissed her, the visions drained out of her with the golden light, leaving the faint taste of pain and loss at the back of her mind.