Sluggish? It could be the garlic (9)
I believe the answer is:
lethargic
'sluggish?' is the definition.
('lethargic' can be similar in meaning to 'sluggish')
'it could be the garlic' is the wordplay.
'it could be' indicates an anagram (I've seen this in other clues).
'the'+'garlic'='thegarlic'
'thegarlic' with letters rearranged gives 'LETHARGIC'.
(Other definitions for lethargic that I've seen before include "lack of energy" , "without energy" , "Lacking in energy or vitality" , "languid" , "Sluggish and apathetic" .)