Dead sluggish! (8)
I believe the answer is:
lifeless
I believe this is a double definition.
'dead' is the first definition.
(synonyms)
'sluggish' is the second definition.
(thesaurus)
(Other definitions for lifeless that I've seen before include "Inanimate or dead" , "Dull" , "Showing no signs of vitality" , "lacking any vitality" , "Lacking animation" .)