Exotic illness? One's held in isolation (10)
I believe the answer is:
loneliness
'isolation' is the definition.
(loneliness is a kind of isolation)
'exotic illness? one's held' is the wordplay.
'exotic' indicates anagramming the letters.
'held' means one lot of letters goes inside another.
'illness' is an anagram of 'lliness'.
'lliness' going around 'one' is 'LONELINESS'.
'in' acts as a link.
(Other definitions for loneliness that I've seen before include "Desolation" , "Feeling of isolation" , "Unwelcome solitude" , "Solitary feeling" .)