"And the curtain of life fell." What is the reference to and how did Douglas happened to be in this position?

William Douglas was drowned by bully into swimming pool.So, on his way down he made a plan to save himself. he planned to reach the bottom and hit the floor ,rise up to the surface of the water ,lie flat on it,and paddle towards the edge of the pool.he tried his strategy twice but all in vain.He didn't lose hope and tried for the third time .He sucked for air but swallowed water and then suddenly all his effort cease. he was feeling peaceful and a sudden blackness surrounded him.He did not panic anymore,he just went to a  deep sleep. He felt as if some tender arms like that of his mother grasped him and he thought that death was approaching him and that he should accept it.So, he commented that "I crossed oblivion and the curtain of life fell''.