Fragmented sentences can be used to add suspense into a novel. Say, if I say something like, "The man's behavior was very odd.", I can also put it like this; "The man's behavior was odd. [different paragraph] Very odd."
Although this was a terrible example, I hope you get was I was trying to say. I'm going to give a better example from my own novel in a moment, but I need to say something first; this part in my novel was shortly after the characters had found a secret message in a note from the King. If you don't know this, this excerpt won't make any sense.
The first night on the road is an exciting on for young adventurers, even if the stakes are high, and feelings are tense.
Aron thought that this was the cause of his sleeplessness that first night, but something was gnawing at his brain, something beyond recall, something about King Ladar's note. He couldn't quite remember, though.
Around midnight, Aron finally began to relax. His last thought before falling asleep was that the hidden message in the note was too obvious.
Far too obvious.
Do you get what I mean now?
One more thing before I wrap this post up. This way of adding suspense should be used VERY sparingly. This isn't a thing that I use every other chapter. It depends on the length of the novel, but at the most, you should only use it once.