The hand rubbing his back was immensely comforting, but he was too far inside his own head to think of saying so. He wasn't even really listening to the Doctor. Just gazing into his own mind and terrified by what he could see there.
"I'm just... too empty. They've gone and there's nothing there to fill the space. I don't know what's supposed to fill the space."
He was trembling again, part-laughter, part-fear. His fingers tightened in his hair, almost pulling it out, trying instinctively to use pain to anchor himself.