Suddenly, The door slamed closed
Suddenly the boy whacked me on the head.
Suddenly, The door slamed closed
No, "suddenly" is not a complete sentence. It is an adverb that describes how an action is performed in a sentence.
Suddenly, my car was under seizure!
I was walking in an companionway and suddenly slip my foot.
The driver suddenly applied the brakes.
Suddenly, the casket fell out of the hearse!
Our boat was suddenly slammed by a transverse wave.
Suddenly, the lights dimmed. She dimmed the lights.
Suddenly, Anubis came around the corner.
The Lithosphere moved suddenly has the Earth moved around.
Suddenly, Titanium Man threw a hammerlock on Magneto.