Normal sleep is required for optimal functioning. Normal wakefulness should be effortless and free of unintended sleep episodes. Problem sleepiness is common and occurs when the quantity of sleep is inadequate because of primary sleep disorders, other medical conditions or lifestyle factors. Medications and substances that disturb sleep, such as caffeine and nicotine, or those that have sedating side effects, may also cause problem sleepiness. This condition can lead to impairment in attention, performance problems at work and school, and potentially dangerous situations when the patient is driving or undertaking other safety-sensitive tasks. However, problem sleepiness is generally correctable when it is recognized. Asking a patient and his or her bed partner about the likelihood of drowsiness or of falling asleep during specific activities, as well as questions that uncover factors contributing to the sleepiness, helps the physician to recognize the disorder. Accurate diagnosis of specific sleep disorders may require evaluation by a specialist. The primary care physician is in an ideal position to identify signs and symptoms of problem sleepiness and initiate appropriate care of the patient, including educating the patient about the dangers of functioning while impaired by sleepiness.