The most common and most likely answer to this crossword clue is the 4 plus 4 plus 2 plus 3 letter word HAVE ANTS IN ONE
H
A
V
E
A
N
T
S
I
N
O
N
E
Buddy explains!
The straight part
We know that "Feel nervous" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case feel nervous = have ants in one.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.