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# Hypersomnolence and circadian rhythm sleep-wake disorders

- Disorder

Being very sleepy despite enough sleep, or sleeping well but at the wrong times because the body clock is out of step with life.

Updated Nov 13, 2026

## Key points

- Idiopathic hypersomnia differs from narcolepsy by the lack of cataplexy, sleep paralysis and hypnagogic hallucinations.
- In idiopathic hypersomnia, the multiple sleep latency test shows short sleep latency (under 8 minutes) without REM periods, and polysomnography shows no other sleep abnormality.
- Delayed sleep phase is typical of adolescents (late to sleep, late to wake); advanced phase is typical of older adults (early to sleep, early to wake).
- Jet lag follows travel across more than two time zones and is worse flying east; non-24-hour rhythm is more common in blind people.
- Light is a strong signal for the clock: a light box on waking shifts sleep earlier and light in the late afternoon or early evening shifts it later; for delayed phase, melatonin is taken 4 to 5 hours before the desired bedtime.
- Before diagnosing idiopathic hypersomnia, polysomnography must show no other sleep disorder, and other medical conditions are ruled out.

## What it is

Idiopathic hypersomnia is excessive daytime sleepiness with difficulty waking and sleep inertia, with or without a long night's sleep (more than 10 hours), when polysomnography shows no other sleep disorder. Circadian rhythm sleep-wake disorders arise when the internal clock is out of line with the schedule a person needs, causing insomnia, sleepiness or both; people have no symptoms when they can follow their natural cycle. Delayed phase is more common in adolescents and advanced phase in older adults.

## Key facts

- Sleep inertia, a period of drowsiness and difficulty waking, is typical of idiopathic hypersomnia.
- In delayed sleep phase, sleep is normal when the person can follow the natural cycle, for example by sleeping late on holidays.
- Shift work symptoms grow with more frequent counterclockwise (sleep-advancing) changes; fixed shifts are biologically preferable, and rotations should go clockwise, from day to evening to night.
- A sleep diary, and actigraphy with a motion sensor worn for 3 to 14 days, show the timing and regularity of sleep.

## Too sleepy, or asleep at the wrong time

| Disorder | Typical patient | Pattern | Treatment principle |
| --- | --- | --- | --- |
| Idiopathic hypersomnia (hypersomnolence disorder) | Sleepy despite enough sleep | Long night sleep in some, difficulty waking, sleep inertia | Wake-promoting medicines |
| [Narcolepsy](https://durgical.com/en/conditions/narcolepsy/) | Excessive daytime sleepiness | Cataplexy, sleep paralysis or hypnagogic hallucinations | Wake-promoting medicines |
| Delayed sleep phase | Adolescent | Cannot fall asleep until very late, cannot wake for school or work | Light on waking, melatonin 4 to 5 hours before the desired bedtime, regular wake time |
| Advanced sleep phase | Older adult | Sleepy in the early evening, wakes very early | Bright light in the evening, light-blocking goggles in the morning |
| Jet lag | Traveller crossing more than two time zones | Insomnia and daytime sleepiness, worse flying east | Light therapy timed to the direction of travel |
| Shift work type | Night or rotating shift worker | Insomnia by day and sleepiness at work | Nap before the shift, light-blocking glasses outdoors by day, dark quiet bedroom |
| Non-24-hour rhythm | Blind person | Sleep times drift later day after day | Melatonin receptor agonists |

## Clinical notes

- Start with a careful history, a sleep diary and a review of drugs, mood and medical illness; refer for polysomnography and a multiple sleep latency test when idiopathic hypersomnia or narcolepsy is suspected.
- Idiopathic hypersomnia is treated with wake-promoting medicines such as modafinil or oxybates.
- For circadian disorders, timing matters: a light box just after waking shifts the clock earlier, while light in the late afternoon or early evening shifts it later.
- Keep regular sleep and waking times, and avoid caffeine within eight hours of the desired bedtime.
- Shift workers may benefit from a short nap before the shift, light-blocking glasses when outside during the day, and a dark, quiet place to sleep.

## Memory aid

Morning light moves you earlier, evening light moves you later: light is the steering wheel and melatonin is the signal for dusk.

## Test yourself

Think of the answer, then tap the question to see it.

## Which clinical features separate idiopathic hypersomnia from narcolepsy?

Idiopathic hypersomnia has no cataplexy, sleep paralysis or hypnagogic hallucinations, and the sleep latency test shows short latency without REM periods.

## A 16-year-old cannot fall asleep before 3 a.m. and cannot wake for school, but sleeps normally on holidays. What is the likely diagnosis?

Delayed sleep phase type of circadian rhythm sleep-wake disorder.

## Which light exposure helps advanced sleep phase in an older adult?

Bright light in the evening, with light-blocking goggles in the morning.

## Why is jet lag usually worse after flying east?

Eastward travel requires advancing the sleep cycle, which causes more severe symptoms than delaying it.

## In whom is non-24-hour sleep-wake rhythm most common?

In blind people, in whom it is more common.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/behavioral-science/hypersomnolence-and-circadian-rhythm-sleep-wake-disorders/)

## Elsewhere in DurgiPedia

- [The pineal gland and melatonin](https://durgical.com/en/physiology/the-pineal-gland-and-melatonin/)
- [Wakefulness, sleep, the EEG and seizures](https://durgical.com/en/physiology/wakefulness-sleep-the-eeg-and-seizures/)
- [Melatonin](https://durgical.com/en/biochemistry/molecules/melatonin/)
- [Promoting sleep in hospital](https://durgical.com/en/nursing/promoting-sleep-in-hospital/)

## Connections

## Related 6

- [How sleep is regulated: sleep pressure, the circadian clock and melatonin](https://durgical.com/en/behavioral-science/how-sleep-is-regulated-sleep-pressure-the-circadian-clock-and-melatonin/)
- [Sleep stages and their EEG](https://durgical.com/en/behavioral-science/sleep-stages-and-their-eeg/)
- [Normal sleep across the life span](https://durgical.com/en/behavioral-science/normal-sleep-across-the-life-span/)
- [Sleep hygiene and the behavioral treatment of insomnia](https://durgical.com/en/behavioral-science/sleep-hygiene-and-the-behavioral-treatment-of-insomnia/)
- [NREM parasomnias and nightmare disorder](https://durgical.com/en/behavioral-science/nrem-parasomnias-and-nightmare-disorder/)
- [Adolescence: development and the HEADSSS interview](https://durgical.com/en/behavioral-science/adolescence-development-and-the-headsss-interview/)

## Related conditions 6

- [Narcolepsy](https://durgical.com/en/conditions/narcolepsy/)
- [Insomnia disorder](https://durgical.com/en/conditions/insomnia-disorder/)
- [Obstructive sleep apnoea](https://durgical.com/en/conditions/obstructive-sleep-apnoea/)
- [Major depressive disorder](https://durgical.com/en/conditions/major-depressive-disorder/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)
- [Dementia (major neurocognitive disorder)](https://durgical.com/en/conditions/dementia/)

## In Pharmacology 3

- [Modafinil](https://durgical.com/en/pharmacology/modafinil/)
- [Sodium oxybate](https://durgical.com/en/pharmacology/sodium-oxybate/)
- [Melatonin](https://durgical.com/en/pharmacology/melatonin/)

[← All of behavioral science](https://durgical.com/en/behavioral-science/)

Educational content on behavior and the clinical relationship; not a diagnostic or treatment guide and no substitute for assessment by a health professional. If you or someone near you is at risk, seek help now from an emergency service or a mental-health helpline.

Sources: [Idiopathic Hypersomnia](https://www.msdmanuals.com/professional/neurologic-disorders/sleep-and-wakefulness-disorders/idiopathic-hypersomnia) (MSD Manual Professional Edition, 2026); [Circadian Rhythm Sleep Disorders](https://www.msdmanuals.com/professional/neurologic-disorders/sleep-and-wakefulness-disorders/circadian-rhythm-sleep-disorders) (MSD Manual Professional Edition, 2026); [Circadian Rhythm Disorders: Diagnosis](https://www.nhlbi.nih.gov/health/circadian-rhythm-disorders/diagnosis) (National Heart, Lung, and Blood Institute (NHLBI), 2026); [Circadian Rhythm Disorders: Treatment](https://www.nhlbi.nih.gov/health/circadian-rhythm-disorders/treatment) (National Heart, Lung, and Blood Institute (NHLBI), 2026).

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Source: https://durgical.com/en/behavioral-science/hypersomnolence-and-circadian-rhythm-sleep-wake-disorders/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/behavioral-science/hypersomnolence-and-circadian-rhythm-sleep-wake-disorders/