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Sleep

Why We Can Misperceive Being Awake or Asleep

Research reveals why we sometimes feel awake even while deeply asleep.

Key points

  • Sleep misperception is a phenomenon in which you subjectively feel awake even though you are objectively asleep.
  • A recent study shows that feeling awake while asleep is more common early in the night, during deep, slow-wave sleep.
  • On the other hand, experiencing vivid dreams was associated with feeling more deeply asleep.

What accounts for feeling deeply asleep?

Sleep researchers and clinicians often compare how someone subjectively reports on their sleep to objective sleep recordings in a laboratory or clinic, and it is not uncommon to find that people have a poor estimate of their sleep, including how long they slept, or the subjective quality or depth of their sleep.

In sleep clinics, patients with insomnia often report feeling like they hardly ever sleep, but after performing a standard polysomnography test, it appears that they have a relatively normal sleep structure. So, what is it that allows someone to subjectively feel deeply asleep?

In a recent experiment, researchers invited 20 good, and 10 poor, sleepers to the laboratory for an overnight study, and used high-density EEG (256 electrodes on the scalp) to record their sleep objectively. The experimenters woke the subjects up repeatedly during the night and asked them whether they felt awake or asleep, and if they felt asleep, how deeply asleep they felt, and whether they remembered any dreaming experience.

The awakenings were performed in different stages of sleep, including NREM (non-rapid eye movement) stage 2, and slow-wave sleep, and REM (rapid eye movement) sleep across the night. At each awakening, the first question asked was, "What was the last thing going through your mind before the alarm sounded?" and then, "Were you awake or asleep?" If the subject felt asleep, they were asked to rate their sleep depth between 1 (shallow) and 5 (deep).

Surprisingly enough, the researchers found that even among good sleepers, in 10 percent of awakenings subjects felt they had been awake even though the EEG showed they were fully asleep. This is called sleep misperception: when you misperceive your sleeping state as wakefulness. The poor sleepers had about three times more instances of sleep misperception.

The experimenters also showed that this state of "feeling awake while asleep" never really happened during REM sleep in healthy subjects, the sleep stage in which we have more vivid dreams.

In the patients, though it sometimes occurred in REM, it was still more common in NREM sleep. Further, this "feeling awake while asleep" seemed to happen more frequently earlier in the night, which was surprising because that’s actually the time period when objectively it appears we have our deepest sleep, with slow waves occurring throughout the brain.

Another interesting point: The researchers found that subjects more often felt awake if they were not dreaming. Contrariwise, when subjects were dreaming, they felt more deeply asleep; again this is more likely to happen in REM sleep, which objectively is a lighter stage of sleep more similar to wakefulness.

It seems like the content of the sleep experience is also important. Sometimes subjects reported just having thought-like experiences prior to the alarm, and often these thoughts were related to trying to fall asleep, feeling like they were unable to sleep, and other similar cognitions.

These thoughts were often reported after being awakened from deep slow-wave sleep early in the night. It’s not clear whether these thoughts are occurring during deep sleep, or perhaps these were the last thoughts the subject had prior to falling asleep, but in either case, upon awakening, subjects had the misperception that they were still thinking about and struggling to fall asleep.

On the other hand, more perceptual dream experiences were associated with the feeling of being deeply asleep, and these more often occurred during REM sleep. In fact, subjective sleep depth directly correlated with dreaming, such that more perceptual and vivid dreams were associated with feeling more deeply asleep.

So to sum up, feeling awake during sleep is not so rare even in good sleepers, and feeling awake during sleep is subjectively very different from feeling asleep. Feeling deeply asleep seems to correlate more with REM sleep and with dreaming experience, and unexpectedly, was less common from deep sleep wave sleep early in the night, which is actually associated with less vivid dreaming, and more thought-life experiences (often about trying to sleep)—and thus associated with feeling less deeply asleep.

References

Stephan, A. M., Lecci, S., Cataldi, J., & Siclari, F. (2021). Conscious experiences and high-density EEG patterns predicting subjective sleep depth. Current Biology, 31(24), 5487-5500.

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