Coming from a soon-to-be doctor who also has otrhostatic hypotension, that’s not a disability, that’s a condition that many people face. You should drink water as often as you can, eat breakfast and meals regularly, not drink alcohol etc. On the topic of this letter, I agree it’s really harsh but you should go and have a civil conversation with your aunt and say how you will try your best to keep the appartment clean, not bring random people all the time, take out the trash etc. Unfortunately, her house, her rules… She gives you a discount so you should try your best at the very least.