Thanks very much for your informative message.

I'm already not thrilled with my cardiologist whose only virtue seems to be he's a very nice, patient guy*. He's just too laissez faire about my symptoms. I had to ask him (i.e. he didn't even suggest it) to order me an event monitor for a week after I developed that inexplicable, persistent tachycardia.
(Inexplicable in that it was unrelated to any normal provocation - activity, stress, alcohol). Even at rest and sleeping, it continued.

I went to the Cleveland Clinic to an arrhythmia specialist and the truth is, he wasn't super helpful either. I had made an appointment to discuss the possibility of having a Watchman procedure (and for particular reasons) . Since while waiting for the appointment, I experienced that protracted tachycardia (which had gone away at least a month before) I wanted to discuss that too. I thought he'd be concerned and have tests or at least, suppositions about it. But no. My echocardiogram was as healthy as it could be* (and I guess that reassured him)

He prescribed the 25 mg Metoprolol. I took it for the first time before I went to the gym, and I nearly passed out much less doing much of anything on the stairstepper.

My pulse dropped instead of rising when I struggled to get ANY workout, and apart from drastic breathlessness by the time I made it home, my blood pressure - normally average - was at most 40/50, while my pulse was only 50 Bpm. One of the worst cardiac experiences of my life. I didn't so much as touch the bottle afterwards I was so traumatized! haha.

It was on this site that I read of one AFIB sufferer who took Metoprolol PRN - the so-called "pill in a pocket" approach. My regular local "general" cardiologist , told me I most certainly could take it PRN and in only the half dose I've been using since.

Yes, it was very effective in reducing tachycardia (especially helpful at bedtime if my pulse s unnaturally high - for me. That is ~ 80 or so. I've learned that's often the precursor to a restless night of constant AFIB)

All this is by way of saying, I really do NOT want to take Metoprolol ER, since I react so violently to it (especially that extreme hypotension and breathlessness).

One thing I've learned in spades from this site is that everyone has, in effect, their OWN version of AFIB. Mine is only minimally symptomatic most of the time (though it can last up to 8 hours).

In contrast, another member gets it only ~ once a year, but on that strange holiday, she is so symptomatic she is rushed to the ER in ambulance, siren blaring! She says it's horrible.

Just for a single contrasting experience.

I guess we all react differently to all medicines. I'm grateful to learn from C ONNECT other people's experiences and what they've learned (and not only about AFIB).
I only wish I could learn a bit more about tachycardia (causes) - I really wish I could understand that protracted episode I described. (FWIW I didn't experience any special symptoms. If it weren't for my Apple watch (confirmed in the ER and later through the Biotel monitor) I wouldn't even have known it was going on!

Hearts certainly are mysterious! And all so individual...

Best of luck to you with your AFIB and heart (and other) health! Also in what you learn about various medications.
🙂