My Mom is 84, has dementia/early Alzheimer, gets herself so worked up now when she is having medial tests. Her blood pressure goes up, when she had her stress test, she made herself sick. Currently she has anemia and we are about to go to a hematologist and I fear more tests that will send her over the edge.
Some people don't like to be touched by strangers, and this could worsen with dementia. Obviously, that can't be helped during a doctor appointment. Let the doctor know ahead of time about your concerns so that he or she can make any adjustments that are possible. If lying down for tests would help, maybe they can do that. My heart goes with you. You may want to check with her primary doctor to see if a mild sedative would be wise. Watching this kind of struggle and the worry that goes with it is one of the hardest parts of caregiving.
Take care,
Carol