Even with the force of the tornado that's just come from the book, you can tell the world you're in is changing dramatically. You're being cast back not just hundreds but thousands of years, and across to another continent and country. New foreign knowledge is flowing into your head of Latin and politics which in your day was ancient history but for your new self is very much current.
But stranger still is what you feel happening to your body. As time flows backward, you and the people who you are descended from are erased from existence, until eventually you reach the point at which you are joined up with people who do exist. Your body is reshaped by their genes, and you soon realize it's transforming. Most obviously, you realize you're changing sex. Your figure changes shape to have more curvaceous hips and narrower shoulders, your skin softens and smooths out, your chest swells as you develop breasts and your penis and testicles recede away until they form a clitoris and ovaries instead. As you feel what had been your scrotum turn into a vagina, you realize you really have been changed into a woman.
As the tornado dies down and you see the new (or old) world around you, you recognise the person you are. Julia Caesar, Empress of Rome.