"My heart aches, and a drowsy numbness pains My sense, as though of hemlock I had drunk" - Who wrote these lines?

- Ode to a NightingaleBy John Keats.My heart aches, and a drowsy numbness painsMy sense, as though of hemlock I had drunk,Or emptied some dull opiate to the drains One minute past, and Lethe-wards had sunk: ’Tis not through envy of thy happy lot, But being too happy in thine happiness,That thou, light-wingèd Dryad of the trees,In some melodious plotOf beechen green, and shadows numberless,Singest of summer in full-throated ease.