Hi Zucchini and John,
Zucchini, my first thought was that it could be from trying to do two things at once.
It's something an OT with a special interest in PD told me not to do.
I think there's some truth in it too.
For me when I'm stumbling (I only have trouble with my gait these days) if someone says something which they usually do like "are you okay" just the simple act of trying to process those words let alone reply is enough to make my stumble worse.
John, do you have tremor dominant PD?
Is it a resting tremor? If so maybe it's pretty standard.
Anyone else have any ideas?
Lee