From one regeneration to the next, certain emotions carried over. Usually it related to some revelation learned just before that moment.
After yet another holiday invasion, the Doctor's clearing mind held two of those great emotions. One was just how strongly he felt for Rose Tyler, and it was hard to watch the edges of her adjusting to his new face and personality. The second was that he'd finally clawed out of the despair from the Time War and could heal.
Perhaps he should have known the two were linked.
Rose had healed him, and her loss nearly destroyed him.