Recover from illnesses, so perhaps rising (9)
I believe the answer is:
repossess
'recover' is the definition.
(thesaurus)
'from illnesses so perhaps rising' is the wordplay.
'from' indicates the answer is hidden within the clue.
'rising' is a reversal indicator (letters written upwards in a down clue).
'ssessoper' is hidden within 'illnesses so perhaps'.
'ssessoper' written backwards gives 'REPOSSESS'.
(Other definitions for repossess that I've seen before include "Regain legal ownership" , "Claim back, for default of payment perhaps" , "Take back (goods)" , "Take back ownership" , "Seize assets" .)