This text comes from The Poetical Works of John Keats, a historical songbook transcribed on Wikisource and reproduced from the pinned revision linked below.
My spirit is too weak; mortality
Weighs heavily on me like unwilling sleep,
And each imagined pinnacle and steep
Of godlike hardship tells me I must die
Like a sick eagle looking at the sky.
Yet 'tis a gentle luxury to weep,
That I have not the cloudy winds to keep
Fresh for the opening of the morning's eye.
Such dim-conceived glories of the brain,
Bring round the heart an indescribable feud;
So do these wonders a most dizzy pain,
That mingles Grecian grandeur with the rude
Wasting of old Time—with a billowy main,
A sun, a shadow of a magnitude.