Longevity

Two hours later, Creed woke up with a numbing soreness over his entire body. He felt as if someone had severely hammered every possible joint in his skeleton. Even moving a finger was flaring an excruciating pain in his nerves.

Raymond had warned him that the pain would be something he had to go through, no matter how strong he was. Everyone has to go through this pain because there are a plethora of changes that happen after drinking the serum.

Not only is his metabolism changing, but the heat radiating from his body is also being stifled. The pain receptors are adjusting to the sudden shuffle. Organs rearranging themselves, radicals going into a hyper-drive, and cells secreting volatile enzymes to avoid fatality. In short, there was a lot of wear and tear going on inside his body right now, and this horrendous pain was just part of the process.