Sudden excitement (6)
I believe the answer is:
thrill
'sudden excitement' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for thrill that I've seen before include "Sudden rush of pleasure" , "Kick" , "Exhilarate, excite" , "Almost pleasant sensation of fright" , "Almost pleasurable sensation of fright" .)