Being no longer able, however, to receive pleasure from the surrounding objects, she soon began to walk with lassitude; the general perceived it, and with a concern for her health, which seemed to reproach her for her opinion of him, was most urgent for returning with his daughter to the house.
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.