fairy I got like this with pressure from work when DD was ill (I was working FT in a pressured place whilst she had cancer. They weren't supportive.) - sometimes your body tells you you need a rest through the way you respond to things. This situation will not get better until he takes a step back from it to allow himself to calm and recover: this is not possible whilst he is still at work.
He needs to get himself to the GP and ask for help. You need to put some gentle pressure on him to go. They should insist on signing him off as he sounds like he needs that time away. Really, your DH should be asking for that anyway. Nobody wants to go off sick, but sometimes we have no choice.
Once he has a rest, a week or two at home, he can reevaluate and put a plan into place. Whether he brushes up his CV and starts looking for other jobs, or sets a time frame in which to do that. He can also start to think about his strengths again rather than all of the things that go wrong. Putting a plan into place is really empowering and lifts you out of the situation: he starts to see it as a step or temporary, rather than all-consuming with no way out. There is always a way out, he just needs to step back.
The GP might give ADs, but this will just be a plaster and will not achieve very much if he is still in the situation and nothing is changing. I take them - I refused to have time off work at first and took them, but my anxiety just kept getting worse. I had a breakdown and 6 weeks off work and then, with rest, the ADs really did make a difference to me and I still take them now. I loves them
but they can't cure a situation. They also make you feel shit for the first couple of weeks you take them, so being at work during that isn't great either.
Other things that are helpful are concepts like 'mindfulness'. There are lots of things online. But, again, I think he needs to be removed from the situation to look into these.
Can he not take holiday if he doesn't want to be signed off?