Why would sharing the nightingales happiness cause Keats to feel unhappy?

Answer 1

Why indeed. The poem "Ode to a Nightingale" is a very personal one describing an actual occasion where Keats sat in his garden, possibly under the influence of drugs, listening to a nightingale. He was very melancholy because he had just seen his brother die of tuberculosis, and having medical training, had realised that he too had the same symptoms of this incurable disease and would soon die the same lingering death. As the nightingale sings Keats floats into a dreamlike state, an out of body experience, where he feels he can fly up and join the nightingale in his eternal song. But he comes to and berates the bird for charming him and asks whether the experience was real or a dream. The nightingale didn't make him unhappy. Quite the reverse, it helped to take his mind off his problems for a while.