Excited and getting overly giddy at first (4)
I believe the answer is:
agog
'excited' is the definition.
(similar in meaning)
'and getting overly giddy at first' is the wordplay.
'at first' suggests taking the first letters.
The initial letters of 'and getting overly giddy' is 'AGOG'.
(Other definitions for agog that I've seen before include "In excited eagerness" , "Impatient" , "Very eager (to hear/see)" , "Eagerly excited" , "Very eager (to see or hear something)" .)