That makes a lot of sense to me - my background is a pretty abusive one, so I learned that reacting would invariably end up with another walloping or if I'd shown any emotion about possessions, I'd be woken up at 1am to them being flung around/at me.
These days, the odds of my getting a battering or my home destroyed are fairly non existent (bar a total breakdown in society) and I'm not trapped in a location or situation where I'd be at risk of that happening, so I'm not having to squash down any fight or flight instincts. And nothing else ever seems quite so bad as not even being able to sleep safely at night. I haven't lost the hyperawareness, I've just lost the 'bad things will happen to me any moment now if I let down my guard and I have to wait for them to happen because I'm trapped here' feeling.
DP had crippling anxiety and really wasn't helped by antidepressants, as they just sapped any energy to do anything about his situation - as I always felt better paradoxically if the abuse happened, rather than waiting for it to happen, I think I'd learned that doing was better than waiting or making myself less able to respond/escape/defend myself, I reframed it as his body was telling him there was something wrong and to RUN AWAY (he's not a fighter) and maybe it could help if he tried literally running away. So I took him out for a slow plod around the park, thinking that the physical exertion would tell his body 'hey, it's OK, we ran away, so the threat has gone'. It actually worked.
It's been a two edged sword in that now there are regular runs and gym visits (weights being more like a fight in terms of lifting heavy bits of metal) for both of us, but he's far, far happier, calmer and doesn't catastrophise or freeze anymore. He also says that now, if there's a disaster, he doesn't freeze, he knows to look for me disappearing off to help/into the distance and follows because we'll either be helping or getting the fuck out of it before anybody else has even noticed there's a problem. 😄