noun
lassitude
LASS-ih-tood/ˈlæsɪtuːd/
A state of tiredness and lack of energy.
The summer heat brings a lassitude that makes work difficult.

Etymology
The pieces express the condition of being weary. Lassitude names weakened energy or languor, applying this tired condition to the mind as well as the body.
In context
They complained of languor, lassitude, want of buoyancy, aching of the limbs, and mental depression.
More examples
- A lingering lassitude kept her on the couch after the flu.
- He shook off his morning lassitude with a brisk walk.
- By midafternoon, lassitude settles over the office.