I think that the role of the vagus nerve in PD needs much greater consideration in light of its relationship to non-motor symptons. It is almost as though it were a bridge between the conscious and sub-conscious minds. It is one of the largest nerves we have and runs from the cranium down into the abdomen, essentially joining the upper and lower bodies. It is deeply involved with our enteric system and can account for constipation and slow gastric problems. It is wrapped up with our emotions as in that tightness in our gut that comes with stress. Also our sexuality as in the Kundalini. Our cardiac system is there too and when we pass out from syncope or orthostatic hypotension the vagus is involved.

When the vagus is "dead", my legs just don't work. This is what I feel when I am coming on. I find that stimulating the vagus can hasten that switch between "on" and "off". There is an implant available but there are also other means ranging from the erotic to the athletic. I will let you work out the details of the former yourself but will share some things from the latter.

Take a time when you are in limbo between on and off. Lie in the floor and elevate your feet on the sofa. Attempt a situp just like back in high school. Don't worry about actually doing one. The important part is to tense as much of the muscle structure in the abdomen as you can. Experiment as to times and so on and see if your transition period is affected.

This is a little-studied area of PD that has a lot of overlap with "non-motor" problems plus a link between critical areas of physical function and emotional storage - the heart ("broken"), the lungs ("took my breath away", the esophagus ("couldn't swallow that one"), the stomach ("fear in the pit of"), the gut ("my gut tells me...") , the lower back , sciatica, the kidneys, sexuality, all are linked by the vagus.