Physical illness involves feeling different, disconnected from the usual experience of possessing control over oneself, having the ability to reason, and considering oneself omnipotent in the world. While unrealistic, feeling all-powerful is needed for it enables one to function in the world, to engage in needed routines without anxiety. Yet this critical sense can be disrupted by physical change, even one so insignificant as suffering a conventional cold or stomach upset for these deny the person the feeling of intactness and affect reasoning.
Suffering a severe illness can be far worse as thinking processes change and helplessness ensue, the latter being the scariest of all feelings: when the ill person becomes passive, and his body no longer respects his commands.