My heart aches, and a drowsy numbness pains
My 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,—
Each of the first three lines has referred to some sense of drowsiness or drugged state. Keats reinforces the melancholic tone through the slow pace of the words, with their long vowels, as in ‘dull opiate’ and ‘drowsy numbness’. It is impossible to read these lines aloud with any speed. 
 The ‘dull’ state is achieved through artificial means, which suggests self-destruction. Well aware of his own mortality, it is unsurprising that Keats fixates on the dulling of his senses. 
