IntroductionWhether daytime sleepiness significantly exists in the chronic fatigue syndrome is presently unclear. The understanding of the underlying physiopathological mechanisms of chronic daytime fatigue like in the chronic fatigue syndrome (CFS) and excessive daytime sleepiness like in the sleep apnea-hypopnea syndrome (SAHS) are still insufficiently explored. Both daytime conditions are generally related to unrefreshing sleep and affective symptoms.MethodsWe studied subjective fatigue by the fatigue severity scale, subjective sleepiness with the Epworth sleepiness scale and objective sleepiness with multiple sleep latency tests. We compared the data of 16 pure untreated CFS without any PSD or psychiatric comorbidity (age, all females) and 13 untreated SAHS (age, all females) patients to 12 healthy controls (age, all females). Affective symptoms were measured with the Beck depression inventory and the Checklist Individual Strength (CIS-20).ResultsMean sleep latency (MSL) was significantly shorter in SAHS patients than in CFS patients and CFS patients showed significantly shorter MSL than age and gender matched controls. Subjective sleepiness was highest in SAHS patients and subjective fatigue was highest in CFS patients.ConclusionsOur data support the clinical distinction between fatigue and sleepiness. Nevertheless patients can combine symptoms and signs of both daytime conditions