Enigma 4

I was once on the brink of doom,
I rode the edge of disaster.
Now am I left delving in gloom,
in dread of what comes after.
Decisive moment: I stood ground,
a shriek flew at limit of sound.
Waist-deep in terrible rescue,
a mirror-lake, a deathly stew.
A shade of evil deeds stares back,
as if devising an attack.
Bearing myself upon darkness,
no chance hope or door to egress.
Demons haunt me at ev'ry bend,
now that I am damned end-to-end.

What am I?