Result of dental anaesthesia overdose? Idiot! (9)
I believe the answer is:
numbskull
'idiot' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
(Other definitions for numbskull that I've seen before include "Dimwit" , "Idiot" , "of limited intelligence" , "Blockhead, bonehead" , "Fool" .)