I feel like I'm going to throw up but I have to go to school!!!?

I woke up this morning feeling extremely nauseous, I went to the bathroom and had diarrhea and haven't been able to stop since, i've gone like five times already. I feel like i'm gonna throw up any second now, but i have to go to school because I have an exam today and review for all my other exams, then more for the next few school days. i do NOT feel up to going to school but I have to cuz my school doesnt let you postpone an exam unless youre deathly ill and have a doctors note and stuff... what do i do!! thanks