Misery ends explosively in SAS (7)
I believe the answer is:
sadness
'misery' is the definition.
(both can mean unhappiness)
'ends explosively in sas' is the wordplay.
'explosively' is an anagram indicator.
'in' means one lot of letters goes inside another.
'ends' anagrammed gives 'dnes'.
'dnes' going inside 'sas' is 'SADNESS'.
(Other definitions for sadness that I've seen before include "Misery" , "Gloom" , "no joy there" , "distress" , "regret" .)