I'd describe it as extreme uneasiness. As though everything is super important and if you happen to do something the wrong way way there will be (unspecified) consequences, yet there is no reward for getting it right.

Even things that shouldn't register at all in your mind feel like a test that you're failing. Stupid things like walking across a parking lot. Inside my head I'm thinking "Are my arms remaining still when I walk? Are people noticing? What do I do with my hands? A car is coming, should I hurry or let them pass? Oh no they stopped for me, now I have to walk in front of them. Did I go too slow? I look stupid jogging" etc etc.

I think all the things my brain should filter out and not have me worry about are instead shoved to the forefront as if they demand my immediate attention. As I try to avoid screwing up in one area it will distract me from another, which then builds the anxiety up. That leads to extreme nervousness, fidgeting, difficulty finding words and speaking properly, shakiness, difficulty breathing...

Even as I'm typing this I went through and changed some words when I noticed I'd used them too many times, because "Oh no, what if someone reads it and I said 'as though' too many times!" It's ridiculous, but it happens whenever I'm in an environment that creates anxiety, which is any time I'm interacting with people.