Actually recover swallowing last of medicine (6)
I believe the answer is:
really
'actually' is the definition.
('really' can be a synonym of 'actually')
'recover swallowing last of medicine' is the wordplay.
'recover' becomes 'rally' (rallying is a kind of recovering).
'swallowing' is an insertion indicator.
'last of' suggests the final letters.
The last letter of 'medicine' is 'e'.
'rally' enclosing 'e' is 'REALLY'.
(Other definitions for really that I've seen before include "In truth - one may be surprised to say it" , "Actually, no kidding" , "Dead" , "In actual fact" , "In genuine way" .)