Sudden fit (8)
I believe the answer is:
paroxysm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sudden fit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for paroxysm that I've seen before include "Sudden uncontrollable outburst - fit" , "Sudden outburst, of coughing say" , "Fit - convulsion" , "Spasm" , "Uncontrollable fit (of giggles, coughing etc)" .)