enervation

noun

1. (countable, uncountable)Act of enervating; debilitation.
2. (countable, uncountable)State of being enervated; debility.

   “His early-morning alertness had gradually given way to bad-tempered enervation as the sun went down, and now his legs dragged, his shoulders slumped as he walked, and even from here I could hear his breath wheezing out of his nose.”