Background: Sleep disturbance is a common problem among patients with Parkinson’s disease (PD). Objectives: To investigate the prevalence of daytime somnolence and night-time sleep disturbances; to characterise the night-time sleep disturbance in patients with daytime somnolence; and to determine the correlation between daytime somnolence and night-time sleep disturbances. Methods: One hundred and sixty patients with PD were included in the study. Each patient completed the Thai version of the Epworth Sleepiness Scale (ESS) questionnaire to evaluate excessive daytime sleepiness (EDS), and the PD Sleep Scale version-2 (PDSS-2) questionnaire to evaluate night-time sleep disturbance. Subjective sleep information and details about the presence or absence of sleep attack (SA) were also obtained from the patients. Results: The types of daytime somnolence found in this study were EDS, SA, and combination of EDS and SA (EDS + SA) with the prevalence rates of 22.5, 3.1 and 6.3%, respectively. The prevalence of night-time sleep disturbance was 46.9%. The most common nocturnal disturbance (82.5%) was “get up at night to pass urine”. There was a significant positive correlation between the ESS score and PDSS-2 total score with a correlation coefficient of 0.16 (p = 0.043). Patients with “EDS + SA” were the most affected by nocturnal disturbances, as they represented the largest group among those patients with night-time disturbances and had the highest PDSS-2 total score (p < 0.05). Conclusion: There are differences in nocturnal sleep disturbances among PD patients with different types of daytime somnolence. The significant positive correlation between the ESS and the PDSS-2 total scores suggests that night-time sleep disturbance may influence daytime somnolence.