The emotional state of Keats was very important in the composition of this Ode. The poet began by detailing his bewilderment at Wentworth Place in Hampstead that morning. At that time he had become consumed by tuberculosis and, as a medical student turned poet, he knew he was near his death, as it had happened to Lord Byron and Shelley. But he celebrated the nightingale's destiny, which will be different from his. He felt heartaches and numbness on his chest as if he had gulped down hemlock or the opiates he was using for his cough. Or as if he had taken a taste of some wine, Flora or listened to a Provencal song. He was happy at the condition of the nightingale because the bird was not going to die. He revered his freedom from mortality and wished to escape to the woods behind the bird, joyful at knowing that it will not suffer what the poet had to endure. He could not see the flowers around him; but he could smell them. Keats admired the nightingale for his immortality. At that moment the bird left and disappeared in the glades and he remained not yet completely convinced if he had had a vision or a waking dream.
Keats's friend, Charles Brown, described how this composition took place:
"In the spring of 1819 a nightingale had built her nest near my house. Keats felt a tranquil and continual joy in her song; and one morning he took his chair from the breakfast-table to the grass plot under a plum-tree, where he sat for two or three hours. When he came into the house, I perceived he had some scraps of paper in his hand, and these he was quietly thrusting behind the books. On inquiry, I found these scraps, four or five in number, contained his poetic feeling on the song of our nightingale. The writing was not well legible; and it was difficult to arrange the stanzas on so many scraps. With his assistance I succeeded, and this was his 'Ode to a Nightingale', a poem which has been the delight of everyone".
Merry Christmas and Happy New Year!