In brief, the proposed study will evaluate a recently proposed naturalistic, driving simulation test to identify and measure sleepiness behind the wheel, one of the most underestimated causes of road accidents. The proposed test offers higher ecological validity and might complement somnological tests that are standard, but rarely performed. Thus, the test might provide traffic medicine and sonologists with an effective tool, that can also directly convey the risks of excessive daytime sleepiness to drivers and thus, in combination, effectively aid in traffic medicine's mandate to avoid preventable road fatalities. Excessive daytime sleepiness (EDS) is a symptomatic condition resulting from too little or compromised sleep, caused by psycho-social stress (shiftwork, lifestyle) or medical conditions (obstructive sleep apnoea (OSA), narcolepsy). Driving with untreated EDS might lead to sleepy/drowsy driving and microsleep, which is considered to be one of the highest-ranking causes of road accidents. Sleepiness and its dangers on the wheel might subjectively not be registered by the affected drivers. Also, subjective sleepiness might not correlate with somnological measurements that are also crucial for legally determining the fitness to drive (FTD). There exists a variety of partially complementary tools to evaluate the extent of EDS. Mean sleep latency obtained in the maintenance of wakefulness test (MWT) is widely, but not uniformly, considered to be one of the most objective measures to evaluate EDS, especially in the context of driving performance. However, there is inconsistent or insufficient evidence for MWTs to reliably predict the FTD in general, potentially as its result might be strongly influenced by motivation. Moreover, patients might not relate low mean MWT-latencies to their own and other's risks in traffic. A need for improved tools to measure EDS was formulated. It remains open, whether the MWT should be replaced or complemented by, for example, future road-side metabolomics-tests detecting sleepiness in traffic or whether the MWT should be adapted to better convey a.) the risks of EDS in traffic and b.) its meaning for the determination of the FTD. With this need in mind the investigators proposed furnishing the maintenance of wakefulness test with improved ecological validity to provide an improved tool for the assessment of the effect of excessive daytime sleepiness on the fitness to drive: recently published results from an exploratory feasibility study suggested it to be well possible to transfer the MWT-paradigm to a driving simulator (DS) with high user acceptance. The published result's implication and relevance was well received: the new test, DS-MWT, might complement somnological MWTs in pneumology and neurology. I might provide a naturalistic and relatable tool to determine EDS in traffic medicine, who is institutionally responsible for determining the FTD. This is also desirable, because prohibitively high cost - in time, money and instrumentation - often prevent a standard MWT in standard care of sleep-related medical conditions. Potentially, the use of the DS-MWT might help reduce the number of preventable road fatalities by more often identifying sleepy individuals before they get behind the wheel. However, for this goal to be achieve, it remains to be evaluated whether the latencies obtained in classical or simulation conditions are comparable and whether obtained latencies actually reflect other clinical parameters of EDS relating to underlying medical conditions, such as for example OSA. This represents a significant gap of evidence for both medical experts in pneumology and traffic medicine, but also for affected drivers. This gap will be filled by systematically comparing classical and simulation-based MWTs by means of their resulting latencies. In a within-study setup of 36 highly adherent OSA-patients, experiments will be related to a main medical comparator, a ≥7-day continuous positive airway pressure (CPAP)-withdrawal (W) and subsequent -resumption or continuation (C), respectively. There will be a control group of 18 healthy participants for comparison.