Catch your breath when grabbed by doctor (4)
I believe the answer is:
gasp
'catch your breath' is the definition.
I can't tell whether this definition defines the answer.
'when grabbed by doctor' is the wordplay.
'when' becomes 'as'.
'grabbed by' indicates putting letters inside.
'doctor' becomes 'gp' (general practitioner**).
'as' put within 'gp' is 'GASP'.
(Other definitions for gasp that I've seen before include "Gaps in struggle for breath" , "Sound of astonishment" , "Convulsive breath" , "Puff, struggle for breath" , "Show amazement" .)