Life ‘Period flu’ is a more ‘severe’ form of PMS. Should you be concerned? April 18, 2022April 18, 2022 Jenna Ryu, USA TODAY Comments Off on ‘Period flu’ is a more ‘severe’ form of PMS. Should you be concerned? Most people are familiar with PMS, but some women are dealing with a more severe batch of symptoms known as the "period flu." What is it?