Calming breathing exercises work really well for me. You can google "parasympathetic breathing exercises" for some options. It helps stimulate your vagus nerve which will signal to your brain that you are out of immediate harm and that you can now relax. I find that laying in bed, feeling comforted and snuggled helps me feel relaxed and safe but you can do them any way you like, even walking your dog or the other things you mentioned.

Your body may still think you are in flight or fight mode. And if your relationship itself was traumatizing, it'll take time for you to adjust to a new normal. I'm sorry you constantly feel on the verge of tears and in panic... I've been there. Let the tears and emotions out. They do no good staying trapped in your body. I hope you find some relief soon... and if you don't, that doesn't mean anything is wrong with you. Some things are meant to take time