Here is what I suggest you say to any medical professional (or other person) who treats you as if you are a 3-year old, just because you are disabled or over 45, black or female or indigenous or lower class.

• “You are committing an epistemic injustice.”
  
• “You are depriving me of my epistemic agency.”
  [or “taking away” or “eroding”]

Feel free to add the word “dear”, “son”, “child”, “sweetie”, “Madam” or anything else that you think fits well, but does not distract too much from the main message. (You want the person to feel puzzled or surprised, off-balance but not personally insulted.)

They won’t expect that and it will likely shut them up for a moment. It may give you a chance to speak and be heard instead of getting tossed out with the trash again.

You have unique knowledge and that knowledge is as valuable as the doctor’s or the nurse’s.

The word “epistemic” is often used in the field of bioethics.

Bioethics is a combination of law, science, medicine, technology and philosophy. (Mentioning philosophy is overkill to some degree as philosophy is part of the foundation of law as well, but few people know that and there is a lot of philosophy in bioethics.)