Is this common practice?

I'm a senior in highschool and I was recently out for 5 days due too a on going medical issue that still hasn't resolved.

Today in my ceramics class my teacher said in order to grade me differently I need to start getting doctors notes or get a medical plan in place to excuse my absences. I was confused no other teacher had ever said this to me, and ask her who is making it so she can't grade me differently and she said her policies don't allow her to do that and it was in her syllabus. I told her I don't think I can get a medical plan, and I don't think I can go back and get excuses for my absences. She was getting red in the face and asked me "how am I suppose to know that your actually sick when it's not in writing?" And I just responded with "I just told you." Which yeah I know dumb response. She then asked me "how come you get held to a diffrent standard then everyone else?" At this point I told her "stop talking to me I don't want to argue or say something bad." and she kept on. This is very brief and I know I wasn't a saint during this conversation I swore at her when she said I'm holding you accountable, I said "you don't hold me to shit." I said more but I was pissed, but I did not call her anything explicit and I said several times stop talking to me I don't want to talk anymore. She sat across from me and wouldn't leave, other students were present during this conversation and wanted her attention but she didn't acknowledge them. Me and this teacher don't get along and I try to avoid her because I love the class.

I don't know what to do, I can get doctors notes but I don't understand why she needs them so bad, I know kids lie but even if I get a note it's not like she can see it. I don't think I can get a medical plan because I don't know what's wrong with me, not like a condition I can point out. The nature of her class is different then most teachers I can't always take home what I'm working on. Sorry for the rant I genuinely have a deep respect for teachers and I don't have a history of conflict with them.