Lethargic (adjective)

1. Lacking energy or enthusiasm; sluggish.
2. Feeling drowsy or sluggish.

Origin:

Late 16c., from french léthargique or directly from medieval latin lethargicus, from greek lethargikos "drowsy," from lethargos "forgetful, drowsy," from lethe "forgetfulness" + argos "idle, inactive".

Examples:

1. The patient was lethargic and had a hard time staying awake.
2. The employee was lethargic and unproductive.
3. The weather was so hot that everyone felt lethargic.
4. The medication made him feel lethargic and he had to stop taking it.
5. The meeting was so boring that everyone felt lethargic and couldn't focus.