One going AWOL in Sahara perhaps, unnerved at heart (8)
I believe the answer is:
deserter
'one going awol' is the definition.
(I've seen this in another clue)
'sahara perhaps unnerved at heart' is the wordplay.
'sahara perhaps' becomes 'desert' (sahara is a kind of desert).
'at heart' means to look at the middle letters.
The central letters of 'unnerved' are 'er'.
'desert'+'er'='DESERTER'
'in' acts as a link.
(Other definitions for deserter that I've seen before include "Renegade" , "Military runaway" , "Traitor" , "Serviceman running away" , "One illegally leaving armed forces" .)