Mood disorder (5)
I believe the answer is:
mania
'mood disorder' is the definition.
(I know that mania is a type of mood disorder)
This is all the clue.
(Other definitions for mania that I've seen before include "Mental disorder that results in excessive or violent responses" , "Aberration" , "Craze; overexcitement" , "A (violent) mood disorder" , "wildness" .)