Valetudinarian (13)
I believe the answer is:
hypochondriac
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">valetudinarian</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 hypochondriac that I've seen before include "Morbidly anxious about health" , "Person with abnormal anxiety about their own health" , "Moliere's eponym" , "Patient with imaginary ailments" , "One who imagines illnesses" .)