Could it be a "One and Done?"

Maybe....maybe not. I am a life-long outdoor guy, runner, cyclist, snowshoer, always ate well, not an unusual amount of stress.....until I fibrillated at the end of a 10 km maintenance run. It wasn't a particularly arduous or unusual run, it wasn't hot....but I began to feel weakness in my legs, they got heavy suddenly, and my breathing changed. An hour later the ER told me I had paroxysmal AF. And that was just the start. I ended up needed two ablations of my pulmonary vein ostia in order to stop it.

It was obstructive sleep apnea. It was the very last of many tests I was subjected to. An over night polysomnography showed I have 'severe obstructive sleep apnea'. Who knew!!

Doctors are told of, and soon enough encounter, 'holiday heart' where a young person has overindulged on a weekend bender (happens, right?) and they present in their local ER with a thumping and irregular heart rhythm. Soon, the heart returns to normal rhythm and that's the end of it...after fluids and rest.

So, your arrhythmia has an indeterminate origin as of now. It may be a one 'n done, or it may return in a few hours or days, weeks, or months. If it returns, and for no apparent reason or stress, then it suggests you have commenced a progressive history with a tachyarrhythmia. You would want to see a cardiologist soon and get a referral to an electrophysiologist (EP), a heart rhythm specialist.

I'm sure you understand that you should hope to, and try to, duplicate any possible circumstances that might have led to the episode while you are being monitored. If you look back and can think of something unusual, and it wouldn't mean endangering yourself, it might be worth trying to get the arrhythmia to repeat.

Isn't 87-90 BPM within the normal range ( 60-100) for a heart rate?

Short answer: Yes. One and done.
After conversion for afib, cardiologist said "Most people don't come back."
(I hoped it was because they were healthy)

@d050526
The dehydration can affect so many things including heart. You not only got dehydrated but then exercised for a long hard level time. Did you sweat during your ride. Drink liquids?

What is your normal resting heart rate? Your pulse was not overly high for doing the exercise you did and for as long as you did. And if dehydrated really could have affected it.

I just wore a 12 lead Holter monitor to see where my PVCs were coming from for a planned ablation on my LV.

I know every time I go to ER the very first thing is to check my electrolytes as has big influence on heart rate, and arrythmia. So not only staying hydrated but the taking in of electrolytes when you exercise and sweat. Most bottle waters (spring) contain electrolytes but you can look the up specifically to see exact amounts.

I had one incident after covid and during a high stress family event December of 2024. None since. Met a new cardiologist who changed my diagnosis to a flutter without talking about it, just saw on my aftercare summary. He has me currently on a holter monitor for 2 weeks, then seeing an EP. I was just thinking the same question and came here to ask, How many people have only had one incident in a long length of time?

@gloaming
I've been avoiding that sleep apnea test. My husband has the whole tube kit and I could never wear all that! Okay...that is on my test list! So appreciative!

@marybird Yes, but it doesn't rule out atrial fibrillation. You can have AF with an HR of less than 90!!! What that lower rate means is that 'RVR', or 'rapid ventricular response' is not currently appearing. When a patient learns they have AF, and that their peak rates are 130-140, it means '... AF with RVR,' which should appear on the written formal diagnosis.

Of course, we would know for certain that it IS AF because of the usual indicators: no P-wave and the R-to-R intervals are all over the place.

@jc76
Thanks. My normal rating heart rate is 54. It's been three weeks now, and so far so good. A mystery. I haven't biked the big hill since my episode, but have been biking nevertheless. I am prone to dehydration. Now, I'm so conscious of it and drink water and diluted tea frequently throughout the day.
I've never been on meds and my Eloquis concerns me. Seeing cardiologist again end of June.

@gloaming I'm very much aware that A-fib can occur with heart rates within the normal range, it's happened to me on occasion. I also understand the physiological role of the AV node in conduction of signals from the atrium to the ventricles in the initiation of a heart beat, as it were, as well as the ratios of the number of signals passed to the AV node by the fibrillating/fluttering atrium to the number that actually get to the ventricles. It's that ratio of signals that get to the ventricles that determine if a person's A-fib is accompanied by RVR, and determines the observed heart rate.

The OP mentioned being dehydrated and having a "racing heart rate" of 87-90 which would seem a little fast if a person's resting heart rate was normally say, in the low 60's, but the racing description is more of a perceived impression, seems to me. There was no mention of A-fib in the post, although I suppose it could be implied from the mention that the OP is now taking Eliquis.