Sudden alarm (5)
I believe the answer is:
panic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sudden alarm</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 panic that I've seen before include "Sudden alarm" , "Have kittens" , "Sudden feeling of terror" , "Horror" , "Sudden infectious terror" .)