Excitement? Yours truly's in a state! (9)
I believe the answer is:
animation
'excitement?' is the definition.
(thesaurus)
'yours truly's in a state' is the wordplay.
'yours truly's' becomes 'I'm' (I'm).
'in' indicates putting letters inside.
'state' becomes 'nation' (both can mean a country).
'a'+'nation'='anation'
'im' inserted into 'anation' is 'ANIMATION'.
(Other definitions for animation that I've seen before include "Film technique; lively state" , "Vigour; film technique" , "Making of cartoons" , "Being full of energy" , "(State of) being full of life" .)