Conflict kept us sleepless essentially (6)
I believe the answer is:
tussle
'conflict' is the definition.
(tussle is a kind of conflict)
'kept us sleepless essentially' is the wordplay.
'essentially' says the answer is hidden in the clue (essence can mean the inside of something).
'TUSSLE' can be found hidden inside 'kept us sleepless'.
(Other definitions for tussle that I've seen before include "Rough and tumble" , "Vigorous struggle or scuffle" , "'Scuffle, rough-and-tumble (6)'" , "Fight vigorously" , "Grapple" .)