Highly excitable one leaves odd souvenir (7)
I believe the answer is:
nervous
'highly excitable' is the definition.
'nervous' can be an answer for 'excitable' (similar in meaning). I am unsure of the 'highly' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for nervous that I've seen before include "Jumpy" , "Edgy" , "Fearful or apprehensive" , "Frightened" , "Jittery" .)