The Black Dragon Ball was created by a man named Baek Yu, a member from the Poison Clan. Baek Yu was master in poison and medicines. When he first made the Black Dragon Ball, he went through many trial and errors. He had to put so much effort in search of the right amount of people, regardless of who it was, to be able to absorb the equal amount of energy through the ball. The important part about increasing internal energy through such medicine was to allow one absorb the power in a stable condition rather than obtain it in large amounts.
The Black Dragon Ball that was created after so many trials was perfected to the point that wouldn't damage the person consuming it. However, even with Yeowun consuming the recommended amount, it made his energy flow explode within him.
Yeowun was drenched in sweat as he meditated through the Sword Force of the Sky Demon. He used the breathing to obtain a greater effect, but moving was much more painful than doing it while sitting down.