Almost reads as if they couldn’t find the cause and heart rhythmic problems would fit. It also is believable.
heart rhythmic isn’t deadly immediatly but if not treated can lead to congestive heart failure,
I had it and it was over a week after diagnosis that they electrocuted me, stopping my heart and then shocked me to re start it.
That’s an inconvenient truth!
It would be believable except everyone said she appeared fine.