What is the author's tone in the poem, Ode to a Nightingale?

The speaker alternates between sadness and ecstasy throughout the poem, wishing to quell the former by means of the latter. He draws inspiration from the nightingale’s “full-throated ease” (10) as he tries to beat back his sorrow, longing to forget “What thou among the leaves hast never known” (22). Though he never imagines himself as a bird per se, the speaker identifies with the bird’s flight, thinking he might join the bird in an escape from human cares by getting drunk, using his imagination, and even by dying. These attempts are unsuccessful, however. In the final stanza, when the bird is “fled” (80) with its music, the speaker is left alone with his “sole self” (72) and his human troubles, finding sadness even in the song he once associated with the bird’s happiness.