Wang Ling circulated the two opposing qi inside his body the way the Extreme Yin Yang Art dictated it to be. The hellish qi and angelic qi that was wrapped with his supreme spirit qi circulated at the same time in his meridians.
There was no uncomfortable feeling when he started the process. But as Wang Ling began cultivating it more and more, it began to hurt.
Wang Ling needed to let the opposing qi go out of the constraints of the supreme spirit qi if he wanted to cultivate this art. But every time he did so, a sharp pain would assault his meridians and the feeling of almost bursting always appears.
This continued as time passed by, becoming increasingly painful as he tried to fuse the two qi into a single entity. The mixing process he did back in the Ancient Creed Mountain was simpler as he only tried to find an equilibrium between the two powers.