Hello Captain Kirk, welcome to the forum.
I was diagnosed in January of this year so still a relative newcomer. Like you, I'd suspected PD for a while before that and was also treated for anxiety (with Citalopram, which didn't help much, and gave me a bad cough - apparently it can have this effect on PD patients!). I'm surprised your PD nurse has suggested you go back on it though, I'm sure I've read that normal anti-anxiety meds don't work when you have PD.
I still suffer from anxiety - as you say, waves of symptoms even with just mild stress. I suspect that my meds make it worse, or even cause it. As Twinks said, PD is weird in that no two people have the same symptoms/severity/progress, so finding a regime that works can take a while. I'm still at that stage and so are you, so don't despair.
It's good that you're still cycling and walking, it's important to stay active (however difficult it can be sometimes!).