She lay half-stretched in an armchair of the living room, crumpled by that heavy, indifferent lassitude which is not the will to laziness, but the frustration of the will to a secret violence that no lesser action can satisfy.
There are no more uses of "lassitude" in the book.
Show samples from other sources
They did not go hunting at all that night, but stayed near the den and rested, The next morning dawned fine and warm, and a general air of contented lassitude seemed to overcome all three.
Farley Mowat -- Never Cry Wolf
In every sense of the word having experienced rebirth, she possessed some of the lassitude and, as a matter of fact, a great deal of the helplessness of a newborn child.