State of mind over ruin (4)
I believe the answer is:
doom
'ruin' is the definition.
(thesaurus)
'state of mind over' is the wordplay.
'state of mind' becomes 'mood' (I've seen this before).
'over' says the letters should be written backwards.
'mood' reversed gives 'DOOM'.
(Other definitions for doom that I've seen before include "In disaster" , "Mood of grim fate" , "Terrible fate; death" , "Condemn to certain destruction" , "Downfall" .)