Holding Pattern

Until I have time to select and post another favorite poem, here is the latest version of my own most recent effort. Thanks to my friend and ace scribe Jim P. for a very helpful comment.

Fled

Fled is that music:—Do I wake or sleep?
And was it the bass or the keening
vocal that kept me awake for two hours
in the first place? And was I ever
really asleep?

Still no takers on identifying the source of the opening line....