exhaustion

n. feebleness, weakness, lack of energy; draining, using up

The word fatigue is used in everyday living to describe a range of afflictions, varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles. It can be both physical and mental. Physical fatigue is the inability to continue functioning at the level of one's normal abilities. It is in everyday life, but usually becomes particularly noticeable during heavy exercise. Mental fatigue, on the other hand, rather manifests in somnolence.
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Exhaustion /ex·haus·tion/ 1. a state of extreme mental or physical fatigue. 2. the state of being drained, emptied, or consumed. [more]Exhaustion - Community and Resources

Noun
1. extreme fatigue
(hypernym) fatigue, weariness, tiredness
(hyponym) inanition
2. serious weakening and loss of energy
(synonym) debilitation, enervation, enfeeblement
(hypernym) weakening
3. the act of exhausting something entirely
(hypernym) depletion
(derivation) run down, exhaust, play out, sap, tire

n. exhaustion, feebleness, weakness