I can’t sleep! Are you sure?

Published: 17-09-2021

Last modified: 24-09-2021

It is estimated that 6% of adults suffer from insomnia. While the problem is real and affects quality of life negatively, it is also known that many people misjudge their sleep time and sleep duration, believing that they sleep worse than objective indicators show. There may be several reasons for this discrepancy.

Insomnia is trouble falling asleep, staying asleep, waking up too early, or experiencing sleep that is not restful. It can occur as the only disorder, but is also often associated with various psychiatric and medical disorders.

Already in the 1970s, when conducting research using a polysomnograph, it was noticed that people complaining of insomnia often overestimate the time spent falling asleep (sleep latency) and underestimated the duration of their sleep. For example, in a study by Carskadon et al. (1977), which was attended by 122 participants, 57 people reported that they slept 5 hours or less each night, although studies showed that only 10 of them had such a short time. 46 patients said it usually takes over an hour for them to fall asleep, and according to the study, this long sleep latency occurred in only 6 people. People who do not complain of insomnia tend to correctly assess their latency and sleep duration.

Although misjudging their sleep is very common among people who see their doctor for insomnia, this does not mean that they do not suffer from insomnia. Some patients say they slept for, say, 2 hours, and research shows that 4 hours, so still too short. However, it also happens that the patient reports sleep problems, and the objective indicators obtained in the study do not show any abnormalities in sleep latency or length.

Why do patients misjudge the quality of their sleep?

There may be several reasons for this. One of them is that people with insomnia may perceive shallow sleep phases as wakefulness. In a study where participants were awake 5 minutes after entering sleep phase 2 or during REM sleep, people with insomnia were more likely to report that just before waking they were not sleeping at all (Mercer, Bootzin, and Lack, 2002 as cited in: Harvey and Tang 2012).

Worrying about falling asleep for too long can misjudge your sleep latency. Time always slows down when we process a lot of information. Therefore, reflecting on what will happen if I do not fall asleep immediately, how I will function tomorrow, etc., can make time subjectively slower, so we get the impression that more time has passed.

Moreover, people with sleeping difficulties often have the habit of checking their watch to see how long they have been awake and how much time they have left until the alarm goes off. Paradoxically, however, checking what time it is has a negative impact on the assessment of the length of time it takes to fall asleep. In one study (Tang, Schmidt and Harvey, 2007 as cited in: Harvey and Tang 2012), people with insomnia were divided into two groups: one was to look at the watch while falling asleep, and the other – at the display showing random numbers. It turned out that the people who checked the time more overestimated their sleep latency. This can be explained by the fact that their brains had to process more information and knowing what time it was they were more stressed that they were still awake, which made time slower for them. It was also noticed that people who looked at their watch experienced more wakings during the first hour after falling asleep. It is possible that the greater stress in these people made it more difficult for them to enter deep sleep phases, and shallow sleep phases, as mentioned above, may be perceived as wakefulness.

Frequent short-term awakenings (lasting between 3 and 30 seconds) are characteristic of many people with insomnia. Polysomnographic studies show that they are more likely to experience short events, such as transitions between REM and NREM sleep phases, and have short periods of awake and micro-arousal (short and transient changes in EEG frequency indicative of wakefulness) during the NREM phases. The duration of sleep is therefore often only slightly shortened, but there are disturbances in switching between sleep and wakefulness. This could be another reason why insomnia patients rate their sleep duration as shorter than they actually are. A person who experiences many short-term awakenings may feel that they have not slept at all during that time.

Persons with insomnia are also characterized by chronic physiological agitation, manifested by e.g. increased heartbeat, increased body temperature, faster metabolic rate. In one study (Bonnet and Arand, 1992 as cited in: Harvey and Tang, 2012), healthy volunteers consumed 400 g of caffeine, 3 times a day for 7 days. In this way, their metabolic rate was increased and symptoms of insomnia were induced. There was a negative correlation between their metabolic rate and their sleep quality, but more interestingly, those with the highest metabolic rate tended to rate their sleep latency as being longer than they actually were. This suggests that also in people struggling with insomnia, the higher metabolic rate may be related to the incorrect assessment of the quality of their sleep.

References

1. Carskadon M. i in. (1977). Self-reports versus sleep laboratory findings in 122 drug-free subjects with complaints of chronic insomnia, American Journal of Psychiatry, 133(12), 1382-1388. (pdf at researchgate.net)
2. Harvey A., Tang N. (2012). (Mis)Perception of Sleep in Insomnia: A puzzle and a resolution, Psychological Bulletin, 138(1), 77-101. (text at nih.gov)
3. Riemann D. i in. (2015). The neurobiology, investigation, and treatment of chronic insomnia, Lancet Neurology, 14,547-558.

Author: Maja Kochanowska