Any idea what could be wrong?

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This is long but our lovely boy has a back story so want to paint a full picture!
We rescued G, a Dalmatian/collie cross at 5YO and he is now 8. He had A LOT of issues when we got him. He was terrified of lots of things: teenagers, bikes, large cars, people with walking sticks, walking anywhere enclosed (ie if the pavement had a wall on one side and parked cars on the other). If he came across any of these things he could freeze and refuse to move. just a very sad nervous dog.

At home he has never shown any signs of separation anxiety, never been destructive or chewed (apart from one day when I couldn't get home before a thunder storm struck)

He's never had any toilet accidents at home. He taps the door when he wants to be let out. Often he will go to bed at 9 and stay there till 10 the next day without wanting to go out.

We run with him every day as we don't let him off lead - recall fine but if he startles he will run and not come back.

He's come on leaps and bounds since three years but would still occasionally refuse to go somewhere if scared.

In the last month he has regressed - been refusing to walk many places he has previously been fine. On Monday DH had to come home from their walk after 20 mins as G refused to walk anywhere. He has also been needing to pee earlier (7am when DH leaves for work)

Yesterday I came home to utter destruction. We have some open stairs down to conservatory. We had lots of boxes underneath with things we never unpacked after moving last year the boxes were torn to shreds, clawed and chewed (with blood around teeth marks) g had pooed on the floor and peed on the sofa.

It was utter chaos. I took G straight out for a run but had to come home after 15 mins as he was a nervous wreck.

So, we're off to the vets today to have him checked out but I thought I'd see if any of you had any experience of something like this. It's awful to see our lovely boy so scared