ER for impending doom?

Everyone says that “no, impending doom due to a medical emergency is WAY different than anxiety impeding doom. you’ll know”. But I don’t believe it, and it scares me.

Has anyone else experienced impending doom so bad that you’ve went to the ER? That it felt like a “certain death” feeling in your body? Has it come in forms of sheer panic and also eerie, terrifying calm?

I’ve experienced these throughout the years and I truly can’t imagine the real thing being so obvious and easy to distinguish 😭