Suspended - highly, if nervous (6)
I believe the answer is:
strung
'suspended' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for strung that I've seen before include "Like violins and tennis racquets" , "suspended" , "Like a violin or racket?" , "Threaded" , "Like tennis rackets and violins" .)