Poor nocturnal sleep is generally associated with daytime sleepiness regardless of the underlying sleep-disrupting condition. A number of studies have demonstrated that patients with insomnia may have significantly disrupted overnight sleep, and yet no significant objective daytime sleepiness as a consequence. Special consideration should be given to mood disorders in the elderly population, and in particular depression. A specific complaint of chronic fatigue could be associated with a relatively poorly defined host of conditions that includes chronic fatigue syndrome (CFS), fibromyalgia (FM), and chronic widespread pain (CWP). Important factors determining the need for treatment of excessive daytime sleepiness (EDS) include chronicity, severity, reversibility in response to adequate overnight sleep, resistance upon demand, impairment of daytime functioning, and danger of (self) injury. A correct diagnosis is an important step, and one must try to tease out the specific complaint, as the fatigue and EDS do not necessarily coincide.