Feeling really ill- should I stay off school?

My head is killing me! + I feel really hot and dizy... I got my retainer back yesterday and it's pulled my teeth and killed my head. I've already been in the shower and had medicine, but I'm feeling no better. My attendance is so low, because I had swine flu and a chest infection + a skin disease, that the school have said that if I'm off for any longer they might have to investigate why. my mum already knew I was feelIng really ill yesterday... What do I do?