Untangling the Riddle

I've used an expression for many years without fully appreciating the depth of it. And maybe you have as well, 'like a canary in a coal mine.' 

Hold the presses! There was a resuscitator. 

"First to fall over when the atmosphere is less than perfect.
Your sensibilities are shaken by the slightest defect.
You live your life like a canary in a coal mine.
You get so dizzy even walking in a straight line."
-bill kenny