It was pain. Searing and sweating pain, and he could've sworn there was an enormous hole in his gut where something should've been---or perhaps it was his brain, where the symbiotic nuclei was implanted. Whatever it was, there was something missing and why couldn't she just see it?

He clung to her, his hands and body slick with sweat of the effort to simply not die or whatever it was that his body was trying to do.

"It's the TARDIS," he hissed against her, "My body's trying to get me to go to the TARDIS, it's been trying to for months, but now it's screaming!"