Doctor sees I'm being sick (6)
I believe the answer is:
emesis
'sick' is the definition.
(I've seen this before)
'doctor sees i'm' is the wordplay.
'doctor' indicates an anagram.
'sees'+'im'='seesim'
'seesim' is an anagram of 'EMESIS'.
'being' is the link.
(Other definitions for emesis that I've seen before include "Vomiting; ie, mess (anag.)" , "Throwing up" , "sick" , "Technical name for vomiting" .)