Valetudinarian (13)
I believe the answer is:
hypochondriac
'valetudinarian' is the definition.
(I've seen this before)
This is all the clue.
(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" .)