Sudden nuisances include a feeling of boredom (5)
I believe the answer is:
ennui
'a feeling of boredom' is the definition.
(ennui is a feeling of boredom or discontent)
'sudden nuisances include' is the wordplay.
'include' indicates a hidden word.
'ENNUI' is hidden within 'sudden nuisances'.
(Other definitions for ennui that I've seen before include "Bored listlessness" , "bore" , "Boredom or discontent" , "Boredom, dullness" , "The feeling of being bored" .)