Isn't one suffering stress? (7)
I believe the answer is:
tension
'stress?' is the definition.
('tension' can be a synonym of 'stress')
'isn't one suffering' is the wordplay.
'suffering' is an anagram indicator.
'isnt'+'one'='isntone'
'isntone' is an anagram of 'TENSION'.
(Other definitions for tension that I've seen before include "A pulling strain" , "Strained state" , "Strain, nervousness" , "Uneasiness" , "Intones (anag) - stress" .)