A recent article in Marie Claire cited a professor of reproductive health at University College London, John Guillebaud, for his statements on period pain.
According to the story, he told Quartz (in this article from 2016) that patients have described the cramping pain as "almost as bad as having a heart attack." About 1 in 5 women have dysmenorrhea, or painful periods, according to the writer of the article. She notes that every month she “spent hours lying on the floor, unable to move, and literally crying out in agony” with pain worse than a slipped disc. Some conditions, such as endometriosis, are known to cause extremely painful periods.