Completely bonkers (7)
I believe the answer is:
berserk
'completely bonkers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for berserk that I've seen before include "Frenzied, maniacal" , "Out of control - in a frenzy" , "Insane" , "Frantic" , "In a violent frenzy" .)