Write a question about the following article.

I woke up with body and stomach cramps and a mild temperature ... oh oh . So I basically ate nothing and spent the day in bed . It proved the right strategy because 24 hours later I was much improved ! In retrospect I had the virus for a couple of days and the muscle pains were part of what made the bed uncomfortable .

Question:
Why is the narrator potentially sore ?
Choose from:
(I). They are suffering from a bad day .
(II). They are suffering from a flu .
(III). None of the above choices .
(IV). They are suffering from a sports injury .