Sleep is an issue in PD because you are also losing cells that produce orexin/hypocretin, the neurotransmitter that causes wakefulness. Your symptoms are the same as people with narcolepsy, sleepy during the day, insomnia at night.

here's a link to the research:
http://neurotalk.psychcentral.com/sh...ad.php?t=25930

I have also written a paper about this, it's on the thread called Narcolepsy, Parkinson's Disease, and Lewy Body Dementia.