Habitual sleeplessness (8)
I believe the answer is:
insomnia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">habitual sleeplessness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for insomnia that I've seen before include "Not getting off" , "Inability to drop off" , "Condition affecting sleep" , "problem at night" , "State of chronic sleeplessness" .)