Say their suffering is mania (8)
I believe the answer is:
hysteria
'mania' is the definition.
(I know that hysteria is a type of mania)
'say their suffering' is the wordplay.
'suffering' indicates anagramming the letters.
'say'+'their'='saytheir'
'saytheir' anagrammed gives 'HYSTERIA'.
'is' is the link.
(Other definitions for hysteria that I've seen before include "Psychoneurotic condition" , "display of wild emotion" , "highly emotional state" , "neurotic disorder" , "Mental disturbance" .)