Encephalitis lethargica, or von Economo “epidemic encephalitis,” the remarkable illness that appeared on the medical horizon as a pandemic following World War I, provided some of the most dramatic instances of pathologic somnolence. Protracted sleep lasting for days to weeks was such a prominent symptom of this disease that it was called sleeping sickness (a term also applied to African trypanosomiasis, as noted below). The patient appeared to be in a state of continuous sleep, or somnosis, and could be kept awake only by constant stimulation. Although the infective agent of von Economo disease was never isolated, the pathologic anatomy was disclosed by many excellent studies at the time, which demonstrated destruction of neurons in the midbrain, subthalamus, and hypothalamus. Patients who survived the acute phase of the illness often had difficulty in reestablishing their normal sleep–wake rhythm. As the somnolence disappeared, some patients exhibited a reversal of the normal pattern, tending to sleep by day, and stay awake at night; many of them also developed a parkinsonian syndrome months or years later. The hypersomnia was theorized to be related to destruction of dopamine-rich neurons in the substantia nigra, resulting in overactivity of the raphe (serotonergic) neurons but how this fits with current models of sleep is unclear.
Hypersomnia is also a manifestation of trypanosomiasis, the common cause of sleeping sickness in Africa, and of other diseases localized to the mesencephalon, and the floor and walls of the third ventricle. Small tumors in this area have been associated with arterial hypotension, diabetes insipidus, hypoor hyperthermia, and protracted somnolence lasting many weeks. Such patients can be aroused; but if left alone, they immediately fall asleep. Traumatic and vascular lesions and other diseases affecting the mesencephalon may have a similar effect.
Confusional awakening, or sleep drunkenness is the name given to a form of hypersomnia, characterized by a failure to attain full alertness for a protracted period after awakening from deep sleep. Unsteadiness, drowsiness, disorientation, and automatic behavior are the main features. This disorder is usually associated with idiopathic hypersomnia, and sometimes with sleep apnea or other forms of sleep deprivation, but often no such connection can be discerned. In a cross sectional study by Ohayon and colleagues using self-reported of symptoms, approximately 15% of individuals were taking medications, particularly antidepressants, or had a psychiatric disorder that may have played a role in the events. It is surprising to us that anxiolytics and soporific agents did not play a larger role.
An interesting type of transient unresponsiveness in elderly patients, as described by Haimovic and Beresford, has been in our experience akin to a deep sleep, but the EEG has not shown sleep patterns.