Transient cessation of breathing (6)
I believe the answer is:
apnoea
'transient cessation of breathing' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for apnoea that I've seen before include "Asphyxia" , "Temporary cessation of breathing, in sleep say" , "Partial suspension of breath, in sleep say" , "Temporary suspension of breath, as in sleep say" , "Temporary suspension of breathing during sleep" .)