I'm not sure ignoring it is exactly the right term I'd use. I think 'accepting' is better.

I've found over the years that it's possible to get into such a state of stress and tension that it's gonna do what it's gonna do no matter what. Once in a while my heart rate will stay up around the 120bpm mark for hours on end, 10-12 hours at least.

Mine does the same as yours J, it'll hover down to about 100 and then if I move or walk around it shoots straight back up to 150.

It'll settle down eventually, but until then all you can do is distract yourself. I also find that it will come and go, up and down. Like you say, don't keep checking it. You know it's fast. Just remember the experiences of the last few weeks and how stress can build up. In some respect having coping mechanisms is a double edged sword as it allows you to absorb more before you feel it hard.