Yes, the anxiety thing is familiar.
I have also recently had that “beat” just above my stomach. Couldn’t work out if it was heart or not – don’t think it could be because it wasn’t in time with my heartbeat – just an irregular sort of twitching? It coincided with lots of muscle spasms in my legs, and I realised it also happened when I was eating less raw veg and more cooked ones (I was having soup for lunch instead of salad). I switched to eating more salad, and particularly having more foods that are high in potassium like avocados and RAW greens, and within a couple of days it has gone away.
Hope that helps!