The entity most opposed to the human race would be the devil, or one of his minions, whether that be fallen angels or demons. Or could it be that he had been so wronged by the members of the human race that his wounded, suppressed subconscious began to seek retribution for the pain inflicted upon him that it created an alter ego to actually execute payback?
As a physician, I have frequently seen that an individual’s manifestation of his afflictions is a result of multiple problems occurring at one time. I have also seen different parts of the body affect each other, including the mind/body interaction and the placebo effect. I have seen people with the same disease die, be healed by medicine or surgery, or healed by the power of God.