Emotional state rejected: that’s fate (4)
I believe the answer is:
doom
'fate' is the definition.
(synonyms)
'emotional state rejected' is the wordplay.
'emotional state' becomes 'mood' (your mood is your emotions).
'rejected' is a reversal indicator.
'mood' backwards is 'DOOM'.
'that's' acts as a link.
(Other definitions for doom that I've seen before include "Day of reckoning" , "Fate; condemn to death" , "Bad destiny" , "In disaster" , "Mood of grim fate" .)