Nervous study I must keep going over (2,4)
I believe the answer is:
on edge
'nervous' is the definition.
(thesaurus)
I can't explain the rest of the clue.
(Other definitions for on edge that I've seen before include "stressed" , "Highly strung" , "Tense and irritable, very nervous" , "Twitchy" , "'Tense, nervous (2,4)'" .)