People with narcolepsy experience excessive daytime sleepiness with sudden attacks of daytime sleep. It is thought to be a sudden attack of REM sleep during the day. These attacks can happen at any time, while on the phone or even driving, and often the person cannot remember things that have happened, like telephone calls. The levels of sleepiness can vary greatly to the point where the condition can be controlled with short naps periodically through the day to the point where it disrupts the persons job, and social life. These patients can also suffer from people thinking they are lazy and unmotivated when actually they have a physiological condition. It is not a psychiatric illness. While the cause is unclear, it does have a heritary component. A trained sleep specialist is required to make the diagnosis, set up an evaluation with polysomnography (an overnight electrographic measurement of the person during sleep) and prescribe treatment, usually some form of medication.