Updated: Jul 24, 2019
One of the biggest frustrations for someone with Idiopathic Hypersomnia is that some people don't believe they actually sleep excessively, or worse that Idiopathic Hypersomnia isn't "real" ... So, do people with Idiopathic Hypersomnia really sleep longer than normal?
The answer is yes. The word “hypersomnia” actually means excessive sleep, not “sleepy”, not “tired” and not even “excessive daytime sleepiness”, but actual sleep that is excessive in depth and excessive in duration. "Hypersomnia means sleep is excessive in depth, deep sleep, can’t wake people up, and excessive in duration, it lasts too long”. 
Numerous studies using objective testing methods ie: 24hr monitoring or actigraphy, have confirmed that people with Idiopathic Hypersomnia sleep longer than is considered normal (more than 8 hours in 24). The longest sleep episode or night time sleep is not always longer than normal however in every case the overall sleep time* in a 24hr period was longer than the controls (people who sleep a normal amount). People with Idiopathic Hypersomnia typically sleep greater than “11 hrs, if not 14-15hr or more in a 24hr period.” [2,3]
*this means the time patients are actually asleep, not just the time in bed.
Research also confirms that the sleep efficiency in patients with idiopathic hypersomnia is typically higher than normal, ie: people with Idiopathic Hypersomnia generally have better than normal quality sleep. Understanding the meaning of hypersomnia is important. ‘Sleepy terms’, such as tired, sleepy, sleepiness, fatigue and excessive daytime sleepiness do not have the same meaning as hypersomnia. People with Idiopathic Hypersomnia can feel tired and physically fatigued just like anyone else and they do experience almost constant excessive daytime sleepiness and mental fatigue, however none of that is hypersomnia. Hypersomnia (excessive sleep, excessive in depth and duration) is the very essence of Idiopathic Hypersomnia, it is its defining feature. Most people can feel tired, fatigued and even at times, excessively sleepy however what sets people with Idiopathic Hypersomnia apart is that they experience all that too, and usually at a much higher extreme, but they also sleep excessively and their sleep is typically deep and long in duration. Also, despite having good quality sleep they often wake up feeling no better than they did prior to going to sleep. In fact waking up is usually extremely difficult. Some say it is the hardest thing they have to do all day. Once they are awake many people with Idiopathic Hypersomnia also experience what is known as ‘sleep drunkenness’*. *sleep drunkenness (i.e; severe sleep inertia): extreme and prolonged difficulty awakening from sleep, confusion, disorientation, irritability and poor coordination with an uncontrollable desire to go back to sleep. It can also be accompanied by automatic behavior (performing tasks without consciously knowing it and not remembering you have done them eg: turning off alarm clocks or answering your phone).
This is from the study “Subjective symptoms in idiopathic hypersomnia: beyond excessive sleepiness” (Vernet and Arnulf, Sleep 2009);
"The Greek-origin word ‘hypersomnia’ means ‘excess of sleep’, which captures one of the main essences of the disease. One may regret that the word hypersomnia has progressively changed meaning to designate many conditions associated with excessive daytime sleepiness, but not with a real excess of sleep (Billiard, 1994). In idiopathic hypersomnia, the sleep excess is best expressed in unrestricted conditions, such as during the weekend, on holidays and in the sleep laboratory, with an average of three additional hours slept. One may notice in this study that the sleep time obtained during long-term monitoring in the sleep laboratory is very similar to the usual sleep time during holidays and on weekends in the patients, suggesting it is not a completely artificial measure, disconnected from true life.” Other relevant references and quotes; “The terms “hypersomnia”, “sleepiness”, and “hypersomnolence” are unfortunately, and incorrectly, used interchangeably.” Rye, D Marigold Foundation/Emory/Univ. Florida collaboration agenda, May 1, 2017, Brain Health Center.
“The terms “hypersomnia”, “hypersomnolence”, “somnolence’, “excessive somnolence” and “excessive daytime sleepiness” are often used interchangeably in the literature. Their definitions can differ considerably from one study to another leading to high heterogeneity in the results and potential for bias.” Hypersomnolence, Hypersomnia, and Mood Disorders, Barateau L, Lopez R, Arthur J, Franchi M, Dauvilliers Y, Hypersomnolence, Hypersomnia, and Mood Disorders, Current Psychiatry Reports February 2017.
“Although sleepiness and fatigue are two different and distinct entities, many patients and unfortunately many medical practitioners are unaware of the complexity and heterogeneity of these symptoms. This may be because some patients use the terms tired, sleepy and fatigued interchangeably and it is difficult to tease apart whether the primary issue is fatigue or sleepiness. The two complaints have distinct implications for clinical diagnosis and treatment.” Measurements of sleepiness and fatigue, Shahida A, Shena J, Shapiroa CM, Journal of Psychosomatic Research, July 2010.
“The term “excessive daytime sleepiness” is often used interchangeably with “hypersomnia.”... hypersomnia is a broader symptom including extended nocturnal sleep, unplanned daytime sleep and an inability to remain awake or alert in situations where it is required (excessive sleepiness). There is also a growing trend in labeling excessive sleepiness as a disease or a disorder. So far, there is no data supporting this claim. Excessive daytime sleepiness is not a disease or a disorder; it is a symptom of a sleep disorder or of another disease.” From wakefulness to excessive sleepiness: what we know and still need to know, Maurice M. Ohayon, Sleep Med Rev. 2008 . Read more: Correct Terminology Matters https://www.hypersomnolenceaustralia.org.au/single-post/2017/09/04/Correct-Terminology-Matters
1. Rye D, 2013 Narcolepsy Network conference, What’s in a Name? Understanding the Origins of the Terminologies for the Family of Hypersomnias.
2. Correspondence with Isabelle Arnulf MD PhD, 12 August 2015
3. Vernet C, Arnulf I, Idiopathic hypersomnia with and without long sleep time: a controlled series of 75 patients, Sleep 2009 Jun; 32(6): pp.753-9.
Vernet C, Leu-Semenescu S, Buzare MA, Arnulf I, Subjective symptoms in idiopathic hypersomnia: beyond excessive sleepiness, Journal of Sleep Research, Volume 19, Issue 4, December 2010, pp. 525–534.
Elisa Evangelista, Regis Lopez, Lucie Barateau, Sofiene Chenini, Adriana Bosco, Isabelle Jaussent, and Yves Dauvilliers, Alternative Diagnostic Criteria for Idiopathic Hypersomnia: A 32-Hour Protocol, Annals of Neurology, Volume 83, Issue 2, February 2018, pp. 235-247
Guilleminault C, Brooks SN, Excessive daytime sleepiness: A challenge for the practising neurologist, Brain, Volume 124, Issue 8, 1 August 2001, pp. 1482–1491.
Roth B, Idiopathic hypersomnia: a study of 187 personally observed cases, 1981 Int Neurol, 15 (1-2), pp. 108-118.
Bassetti C, M.S. Aldrich MS, Idiopathic hypersomnia. A series of 42 patients, Brain 1997, 120, pp.1423-1435.
Billiard M, Merle C, Carlander B, Ondze B, Alvarez D, Besset A, Idiopathic hypersomnia, Psychiatry and Clinical Neurosciences 1998, 52, pp.125-129.
Billiard M, Idiopathic hypersomnia, Neurologic Clinics, 1996; 14: pp.573–582.
Roth B, Nevšímalová S, Rechtschaffen A, Hypersomnia with “Sleep drunkenness”, Arch Gen Psy, 26 (1972), pp. 456-462.
Billiard M, Šonka K, Idiopathic Hypersomnia, Sleep Medicine Reviews October 2016, Volume 29, pp.23-33.
Anderson KN, Pilsworth S, Sharples LD, Smith IE, Shneerson JM, Idiopathic hypersomnia: a study of 77 cases, Sleep 2007, 30, pp. 1274-1281.
Vanková J, Nevšímalová S, Šonka K, Špacková N, Švejdová-Bla¬ejová K, Increased REM Density in Narcolepsy-Cataplexy and the Polysymptomatic Form of Idiopathic Hypersomnia, SLEEP, Vol. 24, No. 6, 2001.
Barateau L, Lopez R, Arthur J, Franchi M, Dauvilliers Y, Hypersomnolence, Hypersomnia, and Mood Disorders, Current Psychiatry Reports 19(2), February 2017.
Rye, D Marigold Foundation/Emory/Univ. Florida collaboration agenda, May 1, 2017, Brain Health Center.
Measurements of sleepiness and fatigue, Shahida A, Shena J, Shapiroa CM, Journal of psychosomatic Research, Volume 69, Issue 1, July 2010, pp. 81-89.
Ohayon MM, From wakefulness to excessive sleepiness: what we know and still need to know, Sleep Med Rev. 2008 Apr; 12(2): 129–141