a dark oscillation

"He longed for her more than he could say. It was a wonderful thing to be able to truly want someone like this--the feeling was so real, so overpowering. He hadn't felt this way in ages. Maybe he never had before. Not that everything was wonderful: his chest ached, he found it hard to breathe, and a fear, a dark oscillation, and hold of him. But now even that kind of ache had become an important part of the affection he felt. He didn't want to let that feeling slip from his grasp. Once lost, he might never happen across that warmth again. If he had to lose it, he would rather lose himself."

Haruki Marukami, Colorless Tsukuru Tazaki and His Years of Pilgrimage