Lassitude is defined as a feeling of lethargy or a lack of mental or physical energy.
When you are in a state where you don't want to do anything except lay around, this is an example of lassitude.
a state or feeling of being tired and listless; weariness; languor
Origin of lassitudeFrench ; from Classical Latin lassitudo ; from lassus, faint, weary: see late
A state or feeling of weariness, diminished energy, or listlessness. See Synonyms at lethargy.
Origin of lassitudeMiddle English, from Old French, from Latin lassitūdō, from lassus, weary; see lē- in Indo-European roots.