Wow that is super-stressful, I am glad both of you are doing better.

I don't know the situation with your grandmother.

However, I help out with an 86 year old friend, who has twice gone to the Emergency Room after feeling dizzy and unwell, and it turned out to be dehydration. Check out this page (Q&A: How to Prevent, Detect, & Treat Dehydration in Aging Adults). It explains why dehydration is a problem in the elderly, symptoms, tips to take to prevent, and more. From that page: "How is dehydration diagnosed? For frail older adults, a simple preliminary check, if you’re concerned about dehydration, is to get the older person to drink some fluids and see if they perk up or improve noticeably. (This often happens within 5-10 minutes.) This is not a clinically-proven method, but it’s easy to try. If drinking some fluids does noticeably improve things, that does suggest that the older person was mildly dehydrated."

Did the emergency people give your grandmother water or other liquid and did she get better? If so, this is why the emergency people may have said she was dehydrated and acted the way they did. They were not uncaring, though it would have helped if they had explained this to you and your grandmother.

After I learned about dehydration in the elderly, my friend (who is not frail) several times has said he is getting dizzy and not feeling well, which has been very concerning to me. I have given him water and each time within 2-10 minutes, he has perked up and was OK and felt well. I have monitored him afterwards, and he was fine. Monitoring afterwards helps, just in case it may be more than simple dehydration.

Again, I am not a doctor and am not diagnosing your grandmother.

For caring your grandmother, you might check out other pages at Better Health While Aging That has helped me.

Best to both of you!