What does the figure of speech his stomach rolls over then settles into a dull churning means?

The phrase, "his stomach rolls over then settles into a dull churning" is a vivid figure of speech that employs strong imagery to depict a feeling of intense nausea. The use of the verb 'rolls' conjures the sensation of the stomach becoming violently agitated, while the subsequent settling into a dull churning conveys the lingering discomfort that follows. The choice of words effectively captures the internal struggle of the character and gives the reader a visceral sense of their distress.