Sweated (8)
(Other definitions for agonised that I've seen before include "Tormented" , "suffered a lot" , "Felt mental anguish (over a decision)" , "suffered torment" , "experienced pain" .)
'sweated' is the definition.
('perspire' can be a synonym of 'sweat')
This is all the clue.
(Other definitions for perspired that I've seen before include "Sweated" , "was sweaty" .)