The elixir left by the dream god.

Morpheus (Μορφεύς) is the god of dreams in Greek and Roman myth. Son of Hypnos, the god of sleep, he possessed the power to shape the human form (morphē, μορφή) at will -- hence his name, "the one who shapes forms." He could appear in the dreams of sleepers and imitate any human likeness perfectly. A dead relative, a vanished lover, a child gone far away -- he could fashion and reveal the image of anyone. Ovid's Metamorphoses contains the most famous episode involving Morpheus. King Ceyx had died in a storm at sea, but his wife Alcyone, unaware of his death, prayed daily at the temple for his safe return. Hera, unable to bear the sight, asked Hypnos, the god of sleep, to reveal the truth to Alcyone, and Hypnos sent his son Morpheus. Morpheus, imitating the dead Ceyx perfectly, appeared in Alcyone's dream and told her, "I am dead; wait for me no longer." Alcyone awoke and was plunged into grief. In 1828, the German chemist Friedrich Sertürner isolated a powerful painkiller from the poppy and named it morphine, after Morpheus -- meaning "the drug that brings dreams."

The Handan Dream (邯鄲之夢) is one of the most famous tales in The Record Within a Pillow, a short story written by the Tang author Shen Jiji. The story goes thus: a poor young man named Lu Sheng (盧生), passing through the city of Handan (邯鄲, present-day Handan in Hebei province), stopped at an inn. In the same place sat a Daoist sage, Lü Weng (呂翁). When Lu Sheng lamented the wretchedness of his condition, declaring that "to gain office and enjoy wealth and glory is the ambition of a man," Lü Weng smiled and offered him a pillow. "Rest on this pillow and take a nap; you will obtain all that you desire." Just then the innkeeper was cooking millet (黃粱). Lu Sheng laid his head on the pillow and fell asleep. In his dream he married the daughter of a wealthy house, passed the civil examinations, became a regional military governor, then chancellor, then the emperor's son-in-law. He lived to the age of eighty, had five sons, all of whom rose to high office. He passed his entire life amid wealth and glory. But in old age he lost everything and met death in sorrow. At that moment Lu Sheng woke from sleep. The inn was just as it had been, Lü Weng just as he had been, and the millet the innkeeper had been cooking was still not yet done. As Lu Sheng gazed blankly at Lü Weng, the sage said, "Life, in the end, is just like this." Lu Sheng bowed deeply and departed, following the Daoist.