Reflex spasm of the diaphragm (6)
I believe the answer is:
hiccup
'reflex spasm of the diaphragm' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for hiccup that I've seen before include "Involuntary glottal closure" , "Temporary setback (colloq.)" , "Snag" , "Minor setback" , "Minor difficulty" .)