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I'm sorry that this is happening. This is a super scary situation to be in. I've had parents with health conditions such as cancer and COPD, and it's hard to watch them go through that.

It might be that your parent is taking their stress out on you. When people are sick sometimes they get really snippy or rude. I'm not saying that this is okay, it just may offer an explanation. Do you think your parents would allow you to talk to their doctor about what is going on so you can get a better understanding of what is going on with your parent and how to try and improve the situation? I know you're still a minor but I've been to appointments with my parents before and it's helped me understand. The doctor probably will be able to say things in a way you would understand.

What about a teacher for a trusted adult, since you're in school? Or a guidance counselor at school? They may be able to offer some support or even host a family meeting with everyone.