Lament hit on head, calling in doctor (6)
I believe the answer is:
bemoan
'lament' is the definition.
(synonyms)
'hit on head calling in doctor' is the wordplay.
'hit on head' becomes 'bean' (bean can informally mean to hit on the head).
'calling in' is an insertion indicator.
'doctor' becomes 'mo' (medical officer).
'bean' placed around 'mo' is 'BEMOAN'.
(Other definitions for bemoan that I've seen before include "Lament, grieve" , "Complain about, lament" , "Regret, lament" , "Deplore, lament" .)