Ugh, I had gastroenteritis back when I was in high school. It was not fun. It lasted about a week, and I HAD to go to summer school (well, I didn't have to go, but wanted to take this one course), and if you missed one day you couldn't come back. My dad went and talked to the VP with a note from the doctor so they let me stay. I just had to sit at the desk closest to the door.
I hope you are feeling better soon.