Use 'lethargic' when describing someone physically drained, like after intense exercise or a long day. After climbing the mountain, she felt lethargic and couldn't walk another step.
Pro Tip 2/3
Emotional State
'Lethargic' can reflect a temporary mood due to factors such as heat or boredom. The scorching sun made the travelers lethargic and unenthusiastic about the tour.
Pro Tip 3/3
Avoid Negative Impression
Calling someone 'lethargic' implies laziness, so use it cautiously to avoid offense. His lethargic attitude during the workshop was mistakenly taken as disinterest.