The slipping to the point of his head paining him being visible was more than he was willing or able to cope with at the moment. He wasn't supposed to be this easy to read. So maybe don't grab your head like it hurts, moron.
He didn't want to say that the more he remembered, the more painful his head became. He didn't want the technician to want to dig around in his brain any more, not now. Not until he had made sense of what was there at the moment.
"Thank you," he said, again. "I will inform you if it continues." But it wasn't as though a dull throbbing in his head was really anything new. Such was the hazard of being a living weapon, wasn't it?