Inclusion Criteria:  Diagnosis of Parkinson's disease consistent with the UK-PD Society Brain Bank Criteria and PD duration at least 1 year with modified Hoehn and Yahr stage 1-3 in the OFF state. Patient reported history of excessive daytime sleepiness (e.g., frequent dozing, nodding, or naps). Anti-Parkinson's medications at stable doses for at least 1 month prior to the Baseline Visit and can maintain a fixed, stable dose throughout the study Epworth Sleepiness Scale score of >10 at screening. Female participants of childbearing potential must test negative in a serum pregnancy test at Screening and have a negative urine pregnancy test at the Baseline and Visit. Women with childbearing potential must use an acceptable method of contraception during the study and for at least 30 days after completion of dosing.  Exclusion Criteria:  Atypical or secondary parkinsonism Significant medical conditions. Evidence of moderate or severe sleep disordered breathing. Drugs that affect sleep including CNS depressants and stimulants. Montreal Cognitive Assessment (MoCA) examine score <24. Hospital Anxiety and Depression Scales (HADS) >11. Have an occupation that requires variable shift work or routine night shifts or travel across two or more-time zones.