Simple: After a long day of work, a deep lassitude settled over me.
Figurative: The news of her failure drained her of all energy, leaving her in a state of profound lassitude.
Descriptive: The summer heat induced a lassitude that made even the simplest task feel overwhelming.
Dialogue: "I'm just too tired to do anything," she sighed, her voice heavy with lassitude.
The best sentence for "lassitude" will depend on the context you're using it in. Consider the tone you want to set and the specific meaning you wish to convey.