Maybe past getting jittery (5)
I believe the answer is:
tense
I believe this clue is a double definition.
'maybe past' is the first definition.
(past tense)
'jittery' is the second definition.
(similar in meaning)
'getting' is the link.
(Other definitions for tense that I've seen before include "On edge" , "Anxious, nervous" , "(Of muscle) tight" , "past possibly" , "edgy" .)