So, I've been carefully documenting my symptoms, doing active stand tests etc and preparing a document to go to my consultant for him to review the meds. Then I realised this morning, after two hours of preparing the documents into a sensible format for him to review, that I have been doing it all wrong and he wanted me to do the stand tests two hours after taking my pill. 
So I'm back to square one and need to do a stand test every evening this week and send the results at the end of the week. Problem being, I will only have a week of the pills left then and really needed the consultant's response to discuss with my GP. 
Not sure what he's going to say to be honest. So far, they seem to be helping a little, in that I am doing ok at a 2 minute stand, but by 3-4 minutes my symptoms kick in pretty hard, probably worse than before the meds to be honest and the bbs aren't stopping my heart rate from shooting up from there. The morning after my second pill I couldn't even stand for 2 minutes without full on pre-syncope and only managed to stop myself going down by a hair's breath. Luckily I was standing by my bed at the time so had a soft landing! 
He could titre the dose upwards, but for the fact my heart rate is dropping as low as 46 in the night and then I get a sudden dropping feeling that wakes me up, followed what feels like an adrenaline rush and all over the body restless legs. Also, my bp has been 83/52 in the night and is generally in the low 90s over low 60s in the day, so I don't think upping the dose would be a good idea from that point of view.
On top of that I've had episodes where my oximeter wave readings have been all over the place, reading a steady heartbeat and SATs, but the wave is really erratic, flatlining, then shooting to max peak, then skipping long beats, then three or four close together. I feel absolutely dire when this happens, struggle to breathe and speak, just out of it really. I suspect some sort of fibrillation or flutter that the oximeter is too basic to pick up, so the heart rate I'm seeing isn't accurate. I managed to get dh to video a couple of these episodes and will take them with me to the cardiologist at the end of the month.
Seriously thinking about telling him to shelve the meds for now and see what I can do with non-pharm measures in the first instance. I'm thinking supplements (need to do some more research on that), recumbent cycle, free weights for arms and compression leggings/tights. I think this is worth a try, not least of all, because I have 4 stone of weight-gain to lose from this latest crash and the beta-blockers could potentially stop that happening.
Oh - and I've had to start salt-loading, as my sample came back as less than a third of the sodium there should have been.