Excitable (5)
'excitable' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for nervous that I've seen before include "On edge, anxious" , "Stirred" , "'Apprehensive, uneasy (7)'" , "Twitchy" , "Jumpy" .)
(Other definitions for hyper that I've seen before include "Abnormally active" , "Slang adjective for over-active or highly-strung" , "Prefix meaning excessively, perhaps active" , "Unable to sit still" , "publicist" .)
'excitable' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nervy that I've seen before include "Highly strung" , "Anxious, jumpy" , "Easily agitated, tense" , "Fidgety" , "Excitable" .)