Something else that needs to be said, which I haven't seen in the thread yet, is that generally speaking, so not this specific instance of OP's DH, it's astonishing how frequently people who are clearly unwell and in the grip of Anxiety or Depression actually have no comprehension of that fact themselves.
This is another common factor in the apparent phenomenon of unwell people seemingly being able to "choose" when they display symptoms of their illness and when they do not.
Take for example someone who is enormously stressed at work, to the point whereby it's a long-term situation that has taken a dramatic toll on their ability to regulate emotion, and they are no longer experiencing adrenalin/cortisol responses in a typical, healthy way. If they have no insight into the fact they are ill, they may well just be under the impression that it is normal, and indeed, common for people to be stressed in the workplace. After all, workplaces are often stressful environments, no?
So despite being chronically anxious, this person doesn't realise they are struggling, because they know no better and just assume this is part and parcel of working life.
They come home, still stressed, still anxious, still experiencing abnormal cortisol responses, and something run of the mill happens, like, for instance, a child being a bit tardy or naughty, or a spouse bringing up an unpleasant piece of necessary but annoying life admin. What happens? a typical response? No, they'll "lose their shit" for want of a better term, because they are ill and they no longer respond in a typical way to typical stimulus.
Do they know why? No, they have no idea they are ill.
Are they "choosing" to act like this? No, of course not, they are unwell.
So you put it to them that they are unwell and need help. "No, don't be silly, I'm perfectly ok, just a bit stressed by work". Well where do you go from there? Of course, they trot off to work the next day, go through the wringer again, and after a while it's not just a case of heightened anxiety, but chronic anxiety and likely a depressed state as well.
I can't stress this enough, but most people have absolutely no insight into their first bout of poor mental health.