Why does keats start the poem ode to a nightingale with question?

The poem "Ode to a Nightingale" by John Keats does not start with a question. It begins with an exclamation:

"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:"