I did something that said something like 50% of PWP are better in the mornings (whether medicated overnight or not), and 50% are worse, unless they've kept the medication up overnight.http://www.scienceomega.com/article/434/sleep-can-benefit-parkinsons-patients-but-we-dont-know-why
I was interested as I am one of the 50% who wakes up almost normal, but if I don't take levodopa straight away the "normalness" wears off within half an hour.
One theory is that dopamine is regenerated overnight (or at least, we're not taxing our dopamine supply so much while sleeping). Another theory is that it's related to cortisol levels, which in everyone are higher in the mornings. (something to do with cortisol being an anti-inflammatory). I certainly think more research in this area could lead to better understanding of some of the chemical processes at the root of PD.