Excessive daytime sleepiness (EDS) is observed in 30 to 50 % of patients with Parkinson's disease (PD) patients, Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA). It is a major complain and represents a socially relevant problem as unintended episodes of sleep can also occur while driving for example. The exact pathophysiology of EDS in PD, DLB and MSA has not been fully elucidated so far, although pharmacological factors (dopaminergic medications) and pathological factors (neurodegeneration of sleep-wakefulness regulatory areas) have been identified. Arterial hypotension is frequently observed in patients with PD, DLB and MSA and considered as a marker of autonomic failure. Sleepiness is known to occur preferentially when patients are having arterial hypotension whatever the cause (i.e. postprandial period, administration of hypotensive medication such as dopamine agonists). We hypothesize that arterial hypotension is associated with abnormal sleepiness. We have observed this association in an on-going epidemiological survey (COPARK Cohort of 800 PD patients, manuscript in preparation). Hyperglycaemia induced by oral glucose load - a standardized model simulating food intake during a meal - provokes arterial hypotension in the majority of Parkinson's disease patients with dysautonomia. It can be hypothesised that sleep attacks in these patients could be mediated by this fall in blood pressure.