Don't know why, but I imagined you were having lots of extra fast heartbeats, so my reply reflected that.
From your reply I see that you have if anything a slow heartbeat, and or missing heartbeats, take the bisoporol, can be a bit of a hit and miss, but if it agrees with you you will find it helps big time.
I didn't mention this earlier, husband has heart failure which is completely different to what I have, the side of his heart muscle is all stretched or blown out, proabaly from a virus which attacked him and he is on bisoporol, works well for him, and he is on a much higher dose than suggested to you.
If your heartbeat continues to fall below 40 again I would not be worring about GP or even waiting for cardiologist appointment, call an ambulance, they will get you on a monitor straight away and hopefully take you to a heart hospital where they can assess what is going on correctly.
Husbands heart fell to 30bpm about a year ago while waiting for appointment with cardiologist, I did not wait, but drove him straight to our city heart hospital, they admitted him and monitored him, his heartbeat fell to 23BPM during the night, the following morning the consultant cardiologist came in looked at his file, listened to what I had to say about what happened, and ordered a pacemaker be installed immediately, some hours later they got it in and husband reported he could breathe the moment they switched it on, previous to that he had problems catching a breath, interesting point is that he also started peeing, LOTS & LOTS, in the few months previous we had been told problems peeing were because of enlarged prostrate, but even that seemed to settle down after pacemaker switched on, when I have mentioned to the dr's we get a shrug of the shoulders, and comment not related, but why the noticeable difference, blood flow, even I can figure that out.