In many patients, the cause of the sleep disorder is apparent from the history and physical examination performed by the sleep specialist and no further diagnostic testing is necessary. This may be the case in patients who take offending medications or in those with clear sleep deprivation, primary insomnia, or medical or psychiatric conditions known to be associated with sleep disorders. In other patients, particularly those in whom the history and examination suggest the possibility of sleep apnea or narcolepsy, additional formal testing in a sleep laboratory needs to be pursued.