noun
languor
LANG-ger/ˈlæŋɡər/
A pleasantly relaxed or weary lack of physical or mental energy.
The resting hiker enjoys a pleasant languor after exertion.

Etymology
Latin languor named faintness or feebleness. English moved from sickness and distress toward weariness and lack of energy, allowing the word to describe pleasant tiredness rather than illness.
In context
Well then the languor is there. A drowsiness diffuses, dimness like a fog envelops consciousness. You get hazy.
More examples
- The afternoon heat fills us with languor.
- She stretches with the languor of someone just waking up.
- After the long hike, languor makes even conversation an effort.
Forms
languorous adjective — Pleasantly relaxed or lacking in energy.