The adjective lethargic means producing laziness, sluggishness or lack of energy.
Synonyms are inert, inactive, dull, or lifeless.
The word origins from the Latin (late 24th century) lethargicus meaning “affected with lethargy”, Greek lethargikos meaning “drowsy”, lethargos meaning “forgetful, inactive” and from 1590s as “pertaining to lethargy”.
The whole class was lethargic after their 3-hour Physical Education class.
She had a fever and was lethargic for two days so they decided to go to the hospital.
It is normal to feel lethargic and super tired at least once a week, but if you think something’s wrong, maybe try visiting a doctor.