Feeling of sickness (6)
I believe the answer is:
nausea
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">feeling of sickness</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 nausea that I've seen before include "Feeling of imminent sickness or upset stomach" , "Feeling of imminent sickness, may be caused by sea" , "Malady" , "Queasy feeling" , "Sick feeling" .)