One of my students attended the final exam, stayed for the full duration, then told me that they were very sick and unable to properly write the test.

I have a make-up exam for students who miss the exam, but this student wrote the test and answered almost every question. They can't just write the same exam again, and I don't have the time to make a brand new test for one student. I wish they had just stayed home.

I don't suspect any shenanigans. They're a very good student and they looked quite sick. Their exam grade was much lower than their midterm grades.

What would you do?