Almost nightly tachycardia w/ other symptoms

So gradually since last august I've been waking up with a rapid heart rate and often acid reflux. My doc gave me lansoprazole for the reflux but hasn't addressed the rapid heart rate yet ( been referred to cardiology on 24th ).

Essentially, I fall asleep and within 2-3 hours I wake up with 150-200bpm..

Sometimes deep breathing can stop it and slow it down but occasionally it just goes on for like an hour or two until it slows down (though heart rate still remains a bit high).

I had some theories that it's post viral (I'm sure I had COVID twice last year) but getting referrals in the UK takes a long time.

It's frustrating now because I'm terrified of sleeping as it seems to come on a lot. There was a period of about a week or two where it seemed to stop a bit but now it's almost every night again.

The ECG never picks anything up because it often calms down by the time the ambulance crews come out etc. Aside from occasional skipped beats since I was a teenager I have not had any heart issues or any family history of it.

My bloods are reported as normal aside from a slightly out of range potassium reading 3.4 as opposed to 3.5 they told me, which they said probably isn't the issue as I could eat a banana and it would put me back into range.

I have been getting some nerve sensations and brain fog too recently which again makes me think COVID or something has messed me up.

Really I'm just looking for reassurance here and maybe some theories because my life has completely came to a halt now. 😟