You have my sympathy MB, it must be very stressful for the whole family. I had a similar situation to your aunt where the paramedics ECG and tests looked normal but took me into hospital just in case. A&E did a further ECG which was OK, but to be safe my doctor then ordered a heart monitor test, which also proved normal.
This was in between cruise bookings, but to be safe I contacted my insurer and gave them the ful details and this is now recorded on my pre existing conditions, and no extra cost was added. So hopefully if I have to claim in future for a heart problem they won't have any reason to invalidate it because it was not disclosed.