He focuses on breathing as she directs and calms down. It helps to know that he hadn't put people in danger by pushing himself too hard.

After he has control again he swallows.

"It... It happened a few years ago. We were travelling home from Orlais. I was meant to be enjoying my time away from university. The darkspawn attacked. They killed my mother and sickened me. My father was convinced that he could have protected us. He blamed himself. That's why letting go of me was so difficult for him. That's why he turned to the Venatori."

He doesn't say it's the Blight, but why else would he be talking about darkspawn?