Question

Was the king really ill? What was the real couse of his sickness?

Answer 1

This line is from the short story/poem/ballad by John Hay, called "The enchanted shirt".

The king was not really ill. He only felt sick. That is all. Actually he had not found happiness and excitation in the world and in his life. He was bored of doing no work and no physical work. All his work was done by others.

So all he had to do was eat, speak and sleep. Somehow he felt something was wrong and something was missing in his life.  So he started feeling sick.  The sickness he felt is common among idle people and people who think they are useless in the world.  

The real cause was his being idle, not doing anything for anybody and not being useful to anyone.