Relief from unconscious thought? (10)
I believe the answer is:
understudy
'relief' is the definition.
(thesaurus)
'unconscious thought?' is the wordplay.
'unconscious' becomes 'under' (as in under anaesthetic).
'thought?' becomes 'study' (study is a kind of thought).
'under'+'study'='UNDERSTUDY'
'from' is the link.
(Other definitions for understudy that I've seen before include "Stage stand-in" , "one covers part" , "one's hoping to get on" , "Replacement" , "One prepared to take over from leading actor" .)