Become ill again (7)
I believe the answer is:
relapse
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">become ill again</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 relapse that I've seen before include "Get into bad habits again" , "causing setback to recovery" , "Deterioration in health" , "Take a turn for the worse" , "Fall back into bad health" .)