Torpor (6)
'torpor' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stupor that I've seen before include "that'll send you to sleep" , "lethargic" , "State of bewilderment" , "State of being dazed or numb" , "Dazed or unconscious condition, sometimes caused by alcohol" .)
'torpor' is the definition.
(I know that lethargy is a type of torpor)
This is all the clue.
(Other definitions for lethargy that I've seen before include "'Lassitude, langour (8)'" , "Stringed instrument" , "Unnatural drowsiness" , "Being sluggish" , "Extreme lack of energy, listlessness" .)