sleep disorder

Sleep disorder can be studied via electroencephalography (EEG), where the brain's electrical activity is monitored by electrodes placed on the scalp. An electrocardiogram or ECG (where the heart's electrical activity is seen) may also be used.

Any of a number of physical or mental maladies disrupting sleep. Sleep disorders range from the rare fatal familial insomnia – an untreatable insomnia that leads to hallucinations and eventually death – to the relatively mild insomnia experienced by almost everyone at times. Sleep disorders are often overlooked by doctors who tend to focus instead on the chronic fatigue they cause. See also snoring.

In 2002, US scientists estimated that of lack sleep in the USA results in a loss of US$35 million to the US economy through accidents and sick pay.