Unusually energetic (5)
I believe the answer is:
hyper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unusually energetic</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 hyper that I've seen before include "Excessively, active, say" , "Really excited" , "Unable to sit still" , "Prefix meaning 'Excessive'" , "Overexcited" .)