What is "nervous"? It's hard to say clearly from a non-physical point of view. But in literature, I think it generally refers to the shock of words and a measure of the sense of picture. Just as the split mirror is to comics and the transition is to movies, it seems unimportant, but it is actually related to the success or failure of the whole work.
I remember seeing a cartoonist, Weibo, before, saying that the function of the comic split mirror is to make the characters' actions in one go, so that readers can feel that the protagonist is moving, and the spaces and words in those cartoons will be "automatically ignored".
The function of comic split mirror is to make readers unable to see the split mirror, and so is the tension of words. The real "text tension" means that the reader can't see the text, but the static or dynamic picture behind the text.
I remember that some literary friends commented on my short story "The Fairy in the Wine" before, especially when the hero had a headache. She circled the whole paragraph and commented: "Emotion and plot have been achieved, but the description is a bit far-fetched." Translated, that is to say, the brain hole is reached and the emotional transformation is reasonable, but the text lacks tension. If you look at it carefully, it is a big reversal. If you look at it roughly, you will only skip it at once. The reader may not realize "Oh, there is a big reversal" at all. Even if I realized it afterwards, the impression I gave was not as good as before.
Wenyou said that she didn't feel wonderful until she read this passage several times, because it was a little rough at first, and she didn't even realize that there was an "important picture" here. Therefore, the tension of words is essential in an article, especially in a narrative like a novel.
As for how to exercise the tension of words, I am also groping. The current thinking is that we can think of a scene, preferably a description of a big scene, such as the appearance or exit of a character, without thinking about the whole story, as long as a detail and an instant picture are described as concretely and delicately as possible.
This method is still in practice. I hope it can work and help me improve my writing.