I am terrified..

So, I have a lot of health problems and that does not make it easy to be physical. Well, lucky me, I have to run a mile tomorrow for PE in under 14 min. but I cannot even walk up a flight of stairs without feeling as if I am going to puke. Last time I tried to run that much, I almost made myself pass out. I ate a lot today and because of that, I am going to get very sick tomorrow, and I just cannot do it. I don't want to wake up in the morning. I don't care if I fail school, they do not understand how much I cannot do this. My mom just keeps telling me to run that fast, but if I do not run faster than I normally do, I will fail my class. I don't know what to do, I am horrified. I really, really just do not want to wake up in the morning.