*Question has been edited to a single question.
Simon clearly suffers from some sort of malady, never specified by Golding, but hinted at throughout the text through details and dialogue. At the very beginning of the novel when the choir boys first arrive on the beach, Jack alludes to the fact that Simon has had previous episodes:
"He's always throwing a faint," said Merridew. "He did in Gib.; and Addis; and at matins over the precentor" (20).
Jack's casual reference to Simon's problem suggests that perhaps the dark-haired boy has some type of epilepsy. He has other similar spells later in the novel, usually brought on by fatigue or the heat. Simon's most pronounced episode occurs in chapter eight during his scene with the Lord of the Flies. The narrator suggests that he faints toward the end of his conversation with the beast when "he fell down and lost consciousness" (144).
Simon's condition makes him both fragile and vulnerable as a character, and most importantly leads to his downfall--Simon is too weakened by the earlier spell to defend himself against the boys' mass attack in chapter nine, ultimately resulting in his death.