The constant rummage through my head is very similar to that feeling you have just before reaching your gate at the airport when you're already running late. You know you're not missing your flight because they find ways to announce this stuff even on silent airports, mostly by screaming it in front of 30 people hoping someone would hold their hand up. No, you're sure that you're in time but that tiny fraction of your brain that still doesn't quite trust anything like the drama queen it is tells you a "what if" so strong you can't really seem to control the rate at which your heart keeps pumping. Somehow that 5 minute run to the gate feels like forever and you're already tired by the time you're there. This time not even primarily because of the bad shape you're in. 

Interestingly, this feeling doesn't exist for me in the vacuum of a badly timed airport visit. These constant jitters (ooh, title card) seep into regular days. This still takes a certain percentage of the total feeling, of course. The rest is like that gutted feeling you have when you've spent the entire weekend doing absolutely nothing and the "rest" you've had just leaves you guilty (and somehow still tired, which I think is just rude).
Now I understand how the feelings I've described aren't novel, this is hardly revolutionary. If someone were to call this 'not revolutionary at all', they'd be right. But I'm just trying to make sense of this very weird combination for you and for me. Did you consider that? No, because you only think about yourself. (Which is fair because that's what I'm doing right now). 

We're getting off topic. 

The reason I decided to write about it is because I have had anxiety for a long time. And a huge chunk of that has been baseless. I have dealt with it and gone back so many times, that by this point it's a routine. I'm not surprised anymore when I wake up with the feeling that "Oh fuck, I'm missing a flight aren't I" as I look ahead at a day with absolutely no travel plans. It's just so very interesting to me how something so unsettling, something that keeps me fidgety all day, and even irritable has slid into a spectrum where it raises no alarms. I have a theory that this is where the gutted feeling comes from. Because when you're anxious you are convinced that you absolutely have to do something. Even if you don't know what it is. And when you don't do "that thing", it feels like you're missing something very crucial. 
But the feeling has just gotten so used to hanging around my head, it doesn't get the guest treatment anymore where I'd run around serving it. 

So since the last time I thought I dealt with it and it came back (shocking), I've been trying to put a lot of thought as to why that happens. Why do insignificant things give me anxiety?

The realisation that set in after all this thought was very weird to accept. I realised I'm the one that's gotten used to the feeling and not the other way around. When I'm anxious, my chest starts feeling very heavy. So heavy that it becomes difficult to notice anything else. Again, since I've felt it for so long, I have convinced myself that it's normal. Which it absolutely is not. So on the days when I suddenly realise that I'm at ease and not feeling heavy, I think about it so much that I fall right into the spiral. At first I thought that's just how it is and I have no control whatsoever. And in some situations, that is the case. But in the rest of the cases, I've actively put my control on a timeout. Now that was hard to accept. 

Since then, I've been trying to figure out how to not trick myself into feeling so unsettled. Are distractions the way to go? Or is it indifference that'll do the trick? 
As of now I have a lot of questions but very little answers. I might've lucked out in the self-awareness department but the self-correction is turning out to be tricky. Do I feel like just letting it be? Absolutely. But one of these days, my entire life is going to turn out to be a series of unsettled feelings and jitters. And why would I actively pick that?

I was hoping all week that by the end of this article, I'd have at least one eureka moment of what I can do. So obviously in the poetic manner of how I like it, writing it down worked out brilliantly. Not the entire solution but a very good start.