A couple of years ago I woke with a minor headache that I ignored for various reasons all day, then skipped lunch as I had an important meeting later and lots to do ahead of it, and the headache got progressively worse. Just before the meeting I felt nauseous, threw up, and then started having the feeling of palpitations in my chest. I've always had them from time to time - that feeling that ones heart has skipped a beat or taken a couple of extra ones - but this time it wasn't going away after a couple of beats.

To cut a long story short, I went to hospital (instead of that meeting) and it turned out that it was atrial fibrillation and that while it feels medium terrifying it's not necessarily that big a deal.

It went away after a couple of days (if it had lasted longer they'd have done "electroconversion" to try to get it back into the proper ryhythm artificially). Apparently the real danger of this is that it might cause a blood clot which in turn could cause a stroke, but it's unlikely to be an issue in the short term.

They did put me on blood thinners and beta blockers between the occurrence and getting a full check up a month later, so I was very calm when we rescheduled that meeting.

Top tip: don't ignore a terrible headache; go to bed.

Edit: PS I think my heart rate was just above 100bpm at rest (possibly 120?), which was unnerving enough, so I can imagine how much more scary 230bpm must feel! You definitely win.