Irregular sleep–wake rhythm (ISWD) is a rare form of circadian rhythm sleep disorder. It is characterized by numerous naps throughout the 24-hour period, no main nighttime sleep episode, and irregularity from day to day. Affected individuals have no pattern of when they are awake or asleep, may have poor quality sleep, and often may be very sleepy while they are awake. The total time asleep per 24 hours is normal for the person's age. The disorder is serious—an invisible disability. It can create social, familial, and work problems, making it hard for a person to maintain relationships and responsibilities, and may make a person home-bound and isolated. Causes ISWD has various causes, including neurological disorders such as dementia (particularly Alzheimer's Disease), brain damage, or intellectual disabilities. It is thought that those affected have a weak circadian clock. The risk for the disorder increases with age, but only due to increased prevalence of co-morbid medical disorders. Diagnosis A sleep diary should be kept to aid in diagnosis and for chronicling the sleep schedule during treatment. Other ways to monitor the sleep schedule are actigraphy or use of a Continuous Positive Airway Pressure (CPAP) machine that can log sleeping times The following are possible warning signs: sleeping off and on in a series of naps during the day and at night, with no regular pattern but with normal total sleep time, difficulty getting restorative sleep, and excessive daytime sleepiness. Because of the changes in sleep/wake time, and because this is a rare disorder, initially it can seem like another circadian rhythm sleep disorder such as non-24-hour sleep–wake disorder or like insomnia. Initial visit with sleep physician A physician specializing in sleep medicine may ask patients about their medical history; for example: neurological problems, prescription or non-prescription medications taken, alcohol use, family history, and any other sleep problems. A thorough medical and neurological exam is indicated. The patient will be asked to complete a sleep diary, recording natural sleep and wake up times, over several weeks. Sleep rating with the Epworth Sleepiness Scale may be used. Medical testing A neurological condition or another medical problem may be suspected, in which case, blood tests, a CT scan or an MRI may be used. An overnight sleep study is usually not needed to detect this disorder, but may be indicated if other sleep disorders, such as sleep apnea and periodic limb movement disorder, seem likely.