The most common and most likely answer to this crossword clue is the 7 letter word SHARPLY
I've seen this crossword clue in The Daily Telegraph
S
H
A
R
P
L
Y
More clues leading to the result SHARPLY
Buddy explains!

The straight part
We know that "suddenly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case suddenly = sharply.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.
What does SHARPLY mean?
SHARPLY adverb- In a sharp manner.
- (to describe breathing) Suddenly and intensely like a gasp, but typically as the result of an emotional reaction.
- In an intellectually alert and penetrating manner.
- Severely.
- Of speech, delivered in a stern or harsh tone.