My DS is very like this. It's to do with when they're so dysregulated it's almost like they have dissociated. I call it "Gone to planet DS" and I actually think it is a kind of overwhelm. He processes everything in extremely high detail, and so it's almost like he's processed so many things that he has gone over some limit of living in reality and has gone into gaga land. (And yes he was assessed for autism, but the ADOS found no signs).
It is wearing because I can't address behaviour in the moment because he escalates so extremely that it's really all just de-escalation and keeping everyone safe.
If he's not totally sky high on a rocket blast and about to explode (his entire body is tense and wiry and his heart is going 10000 mph) then it's no use talking to him close to the moment anyway because he's not engaging - he's in his own world.
But then trying to talk about it afterwards is no use either because it's like he can't conceptualise a past event now that it has finished. This is getting a tiny bit better now he is older - but still, while he can now recall a past situation, the gap where he's neither exhausted, nor escalated by something else, nor overexcited by something is very small and doesn't always leave time for talking about behaviour. When we can catch that it feels like we get somewhere, but doesn't always translate into action, so very slow progress overall.
I think he is constantly at a low level of stress and trying to figure out what the causes of that are so we can alleviate any of it is the puzzle now. Looking to get him into OT, but there are waiting lists.
We've also had some input from speech therapy because he had some pronunciation issues and because we are in a non-English speaking country so he has had assessment due to not being a native speaker of the local language. They have suggested that we look into auditory processing disorder, which we may do (but he was having so many tests at that time we didn't want to put him through more, esp as APD doesn't "open any doors" as such in this country). I think in the UK it's less likely this would be flagged up unless you wanted to bring it up with a GP.
Honestly he is so very different to DS1 that it's a whole other ball game, although DS1 was like this, it wasn't as constant or extreme. But it is easier having DS1 as a handy reminder that while it was hard when he was younger he did grow out of it.