Idiopathic Hypersomnia (IH)
My take…Idiopathic - unknown reason Hypersomnia - sleeps too much
Over the past 20 years, I have been self studying and learning about sleep architecture and sleep disorders. I found this article a nice overview for people trying to learn more about IH and how it differentiates from Narcolepsy. Unfortunately, I cannot provide the source, but I still wanted to share.
Many people feel they sleep too much and want to know what is wrong. What can they do about it? The answer is to seek evaluation with a sleep specialist, undergo an overnight sleep study to find the answer. Before my apnea was diagnosed, I thought I slept too much, sleeping my life away. After my sleep study, the apnea was clearly revealed and successfully treated. While I thought I was sleeping 10 hours a day, I was actually only getting 2 - 3 hours of sleep, the remaining hours were actually apnea events robbing me of oxygen and quality sleep.
So, if you feel you sleep too much, let your doctor know and be evaluated properly with an overnight sleep study.
Hypersomnia (EDS or excessive daytime sleepiness) is defined as recurrent daytime sleep episodes for at least 3 months. Narcolepsy and IH can be difficult to distinguish based on symptoms alone unless Cataplexy is present. A sleep study is necessary to distinguish one from the other.
Both N and IH are characterized by EDS - excessive daytime sleepiness - and frequent napping. While variations are seen, N and IH differ in a few important ways. IH does NOT include the other symptoms of N, namely cataplexy, hypnagogic/hypnopompic hallucinations, sleep paralysis and disrupted nighttime sleep.
IH is typically characterized by deeper and more prolonged sleep in comparison to N. A person with IH will sleep 12-14 hours or longer without waking, and has difficulty waking up. In contrast, a person with N usually can’t sleep more than a few hours without waking, often feeling fully alert.
Typically, an overnight sleep study of a person with narcolepsy shows a sleep latency of less than 5 minutes and a REM sleep latency of less than 10 minutes. The overnight sleep study of a person with IH shows a sleep latency of less than 10 minutes but a normal REM latency (approx. 90 minutes).
The MSLT or Multiple Sleep Latency Test results of a person with narcolepsy will reflect a sleep latency of less than 5 minutes, with sleep-onset REM in two or more naps. The Multiple Sleep Latency Test of a person with IH will reflect a sleep latency of less than 10 minutes, with fewer than two naps showing sleep-onset REM.
Subjectively, people with narcolepsy tend to alternate between periods of wakefulness and sleepiness, during the daytime as well as the nighttime, while a person with IH rarely if ever feels fully alert or refreshed, no matter how long they sleep.