The most common and most likely answer to this crossword clue is the 4 plus 6 letter word YOUR BREATH
I've seen this crossword clue in The Guardian
Y
O
U
R
B
R
E
A
T
H
Buddy explains!
The straight part
We know that "Don’t hold it, because it won’t happen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case don’t hold it, because it won’t happen = your breath.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.