Use 'languid' to describe someone's temporary lack of physical or mental energy, not their overall personality. After the marathon, the runners appeared languid and exhausted.
Pro Tip 2/3
Avoid Negative
'Languid' can be used negatively, but it's less harsh than 'lazy', focusing on the current state. Her languid demeanor at the party was due to her tiring week.
Pro Tip 3/3
Not Always Illness
While 'languid' can imply illness, it's also used for a normal state of tiredness or relaxation. The languid summer afternoon made everyone feel relaxed and unhurried.