So what is sleep inertia? “Sleep inertia” refers to the transitional state between sleep and wake, marked by impaired performance, reduced vigilance, and a desire to return to sleep. The intensity and duration of sleep inertia vary based on situational factors, but its effects may last minutes to several hours.” [1] In simple terms sleep inertia is when you find it extremely difficult to wake up. People with severe sleep inertia sleep through alarms and may even fall back to sleep several times. They often require humans to wake them and to make sure they stay awake. People with idiopathic hypersomnia who have sleep inertia usually experience it every time they wake up ie: in the morning and when waking up from naps. And what is sleep drunkenness? Sleep drunkenness consists of confusion, disorientation, poor motor coordination, and slowness [1,2]. People with sleep drunkenness may say irrational or unintentional things. Their speech may be slow or slurred. They may be clumsy eg: drop things, walk into doorways or bounce off walls. Some people report sleep drunkenness lasting as much as 4 hours or more and that it can “sometimes be more problematic than the daytime sleepiness (experienced in IH) ” [1].
The following description is of people with Idiopathic Hypersomnia who experience sleep inertia and sleep drunkenness. The yellow highlighted text is the sleep inertia and the green highlighted text is the sleep drunkenness. “Patients rarely waken spontaneously at an appropriate time; they have to be awakened. They usually do not awaken to the ringing of a clock or telephone, or, if the ringing is prolonged, they shut it off and return to sleep. Many patients have special devices for waking them up such as repeating alarm clocks and resonators. In most cases, these devices are ineffective, and the patients have to be awakened by their family members. Awakening procedures must be vigorous and persistent; it is usually necessary to shake the patient repeatedly before he reacts. Even then the patients are confused, disoriented, very slow, and unable to react adequately to external stimuli. If left alone, they often return to sleep and later do not remember having been previously awakened.” [3] According to these distinctions, someone can have sleep inertia (extreme difficulty waking up) but if they are not clumsy, confused and unable to react adequately to what is going on around them then it is not sleep drunkenness. Difficulty awakening from sleep (sleep inertia) is common in healthy people, especially in adolescents (42% of adolescents report difficulty getting up almost every morning) [1]. Sleep inertia is also not uncommon in several medical conditions, such as sleep deprivation, delayed sleep phase syndrome, non-rapid eye movement (NREM) arousal disorders, sleep apnea, insomnia, and mood disorders although it is less frequently seen in narcolepsy type 1 (with cataplexy) [2]. While regular healthy people and people with medical conditions including other sleep disorders may experience sleep inertia and/or confusional arousals researchers that have studied idiopathic hypersomnia suggest the extreme difficulty waking up (sleep inertia) and sleep drunkenness seen in people with idiopathic hypersomnia is typically much more severe than the sleep inertia and confusional arousals that occur in other individuals. Extreme difficulty waking up (sleep inertia) and sleep drunkenness have been noted as “highly specific (in IH), as clear-cut sleep drunkenness is not found in controls”. [4] This is from the paper “Waking up is the hardest thing I do all day: Sleep inertia and sleep drunkenness” [1] “The syndrome of “hypersomnia with sleep drunkenness” was proposed by Bedrich Roth based on patients examined since the 1940s. In 58 patients, he described sleep drunkenness manifesting as confusion, slowness, incoordination, and a tendency to return to sleep lasting up to 4 hours, which was sometimes more problematic than daytime sleepiness itself. Such sleep drunkenness was much more severe than the physiologic sleep inertia that occurs in healthy individuals, with patients often requiring the assistance of another person to be able to wake up. During the period of sleep drunkenness, hypersomnia patients exhibited ataxia (the loss of full control of bodily movements), orthostatic disequilibrium (unsteadiness, imbalance when getting up), and hyporeflexia (muscles have a decreased or absent reflex response). Roth ultimately concluded that this syndrome was a variant of idiopathic hypersomnia and reported a frequency of sleep drunkenness of 55.1% in idiopathic hypersomnia. Subsequent clinical series have confirmed the high rate of sleep drunkenness in this disorder”. So how common is sleep inertia and sleep drunkenness in people with idiopathic hypersomnia? In the paper “Narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time: a cluster analysis” 40% of people with IH without long sleep had great difficulty waking up whereas 97% of people with IH with long sleep experienced great difficulty waking up. In the same paper 58% of people with IH with long sleep had sleep drunkenness however none of the people with IH without long sleep had sleep drunkenness [5]. A paper published recently, “Sleep inertia measurement with the psychomotor vigilance task in idiopathic hypersomnia” found sleep inertia was common (92%) in IH however only approx. 24% of people with IH have sleep drunkenness (all the people with sleep drunkenness also had sleep inertia) [2]. Note: of the 62 patients with IH in this study only 5 had IH without long sleep (3 with mild and 2 with severe sleep inertia. None of them had sleep drunkenness). This is from the introduction of that paper: "Idiopathic hypersomnia (IH) is an orphan hypersomnolence disorder clinically characterized by three main symptoms: excessive daytime sleepiness (EDS), excessive quantity of sleep (EQS), and sleep inertia. Sleep inertia refers to the difficulty to wake up and “getting going” after sleep (reduced vigilance and impaired performances), lasting from few minutes to hours. Sometimes, patients may be also confused and unable to react adequately to external stimuli on awakening, a condition called sleep drunkenness. In IH, sleep inertia and sleep drunkenness are frequent (21% to 55%) and may be severe and disabling, resulting in a significant impairment of the quality of life."
And this is from the discussion: "Sleep inertia is a frequent and disabling symptom in IH, but it is often underestimated by physicians, and is not included in the ICSD3. In IH, sleep inertia may be severe and long lasting, and is sometimes associated with confusion, disorientation and clumsiness (i.e. sleep drunkenness that may be more problematic than the excessive daytime sleepiness) … Here, we found 91.9% with IH reported sleep inertia. Sleep inertia was severe (i.e. frequent and for a duration ≥30 minutes) in 56.5% of patients with IH among whom 24% reported also in line with previous studies. Both symptoms were more frequent in IH than in the other group (those with other sleep disorders), with low frequency in patients with NT1 (narcolepsy with cataplexy). Patients with obstructive sleep apnea and insomnia are more likely to report fatigue and confusion at awakening, potentially linked to chronic sleep fragmentation. Conversely, in NT1, nighttime sleep and naps are often refreshing with infrequent sleep inertia. Our study extended these findings by highlighting the frequent occurrence of severe sleep inertia with/without sleep drunkenness in patients with IH… Sleep inertia in IH has less fragmented nocturnal sleep (than those with other sleep disorders), as previously reported in patients with IH. Accordingly, patients with IH had the largest frequency and duration of sleep inertia, but also of undisturbed nocturnal sleep. Laboratory studies on healthy subjects found that cumulative disrupted sleep and sleep deprivation are associated with increased sleep inertia. Similarly, sleep inertia reported by patients with obstructive sleep apnea and insomnia have been linked to sleep fragmentation and sleep restriction… The reason for the severe sleep inertia in IH is poorly understood … it has been hypothesized that awakening difficulties in patients with IH could be explained by a tendency toward a delayed sleep phase and excessive need for sleep that cannot be fulfilled, resulting in sleep deprivation. We recently reported higher sleep efficiency and a trend to higher percentage of slow wave sleep in patients with IH, and proposed a standard for the diagnosis of clear-cut IH that requires normal sleep continuity and architecture." The researchers are pointing out that the reason people with other sleep disorders experience difficulty waking up and confusion at awakening is likely due to chronic sleep fragmentation (poor quality sleep). Poor quality sleep and lack of sleep (sleep deprivation) has also be found to be associated with sleep inertia in healthy people . People with IH however do not have poor quality sleep. In this study and in others [6-8] it has been shown that people with IH have a higher quality of sleep and longer duration with a tendency towards more slow wave (deep) sleep than even healthy people do. This suggests that the underlying cause of sleep inertia and sleep drunkenness in IH may not be the same as it is in other individuals. It is possible, and has been discussed in this paper and others [2, 9-13], that people with IH may have a delayed sleep phase and that because people with IH have an insatiable need for sleep (an excessive need for sleep that cannot be fulfilled) this results in sleep deprivation (despite a huge amount of sleep) and that this could be the cause of the extreme sleep inertia and sleep drunkenness in IH. We look forward to more research in this area. References: 1. Trotti LM. Waking up is the hardest thing I do all day: Sleep inertia and sleep drunkenness. Sleep Med. Rev. 2017;35:76–84. 2. Evangelista E, Rassu AL, Lopez R, Biagioli N, Chenini S, Barateau L, Jaussent I, Dauvilliers Y, Sleep inertia measurement with the psychomotor vigilance task in idiopathic hypersomnia, Sleep. 2021; zsab220.
3. Roth B, Nevsimalova S, Rechtschaffen A. Hypersomnia with "sleep drunkenness". Arch Gen Psychiatry 1972; 26: 456-62.
4. Vernet C, Leu-Semenescu S, Buzare MA, and Arnulf I. Subjective symptoms in idiopathic hypersomnia: beyond excessive sleepiness. J Sleep. Res. 2010; 19: 525–534. 5. Sonka K, Susta M, and Billiard M. Narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time: a cluster analysis. Sleep Medicine. 2015; 16: 225–231. 6. Leu-Semenescu S, Quera-Salva MA, Dauvilliers Y. French consensus. Idiopathic hypersomnia: Investigations and follow-up. Rev Neurol (Paris). 2017 Jan-Feb;173(1-2):32-37. doi: 10.1016/j.neurol.2016.09.015. Epub 2016 Nov 10. PMID: 27838089.
7. Evangelista E, Lopez R, Barateau L, Chenini S, Bosco A, Jaussent I, Dauvilliers Y. Alternative diagnostic criteria for idiopathic hypersomnia: A 32-hour protocol. Ann Neurol. 2018 Feb;83(2):235-247. doi: 10.1002/ana.25141. Epub 2018 Feb 9. PMID: 29323727.
8. Evangelista E, Rassu AL, Barateau L, Lopez R, Chenini S, Jaussent I, Dauvilliers Y. Characteristics associated with hypersomnia and excessive daytime sleepiness identified by extended polysomnography recording. Sleep. 2021 May 14;44(5):zsaa264. doi: 10.1093/sleep/zsaa264. PMID: 33249509. 9. Vernet C, Arnulf I. Idiopathic hypersomnia with and without long sleep time: a controlled series of 75 patients. Sleep 2009;32(6):753–759.
10. Materna L, Halfter H, Heidbreder A, et al. Idiopathic Hypersomnia Patients Revealed Longer Circadian Period Length in Peripheral Skin Fibroblasts. Front. Neurol. 2018;9:424.
11. Sforza E, Gaudreau H, Petit D, Montplaisir J. Homeostatic sleep regulation in patients with idiopathic hypersomnia. Clin. Neurophysiol. Off. J. Int. Fed. Clin. Neurophysiol. 2000;111(2):277–282.
12. Pizza F, Ferri R, Poli F, et al. Polysomnographic study of nocturnal sleep in idiopathic hypersomnia without long sleep time. J. Sleep Res. 2013;22(2):185–196.
13. Landzberg D, Trotti LM. Is Idiopathic Hypersomnia a Circadian Rhythm Disorder? Curr. Sleep Med. Rep. 2019;5(4):201–206.