Mental dullness (6)
I believe the answer is:
stupor
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mental dullness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(stupor means a dull state of mind)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for stupor that I've seen before include "State of shock" , "Inertia results!" , "State of insensibility or near-unconsciousness" , "Semi-comatose state" , "Semi-conscious state" .)