Sleep notes
Do You Only Dream in REM Sleep? What Research Shows
By ToSleep AI · 2026-10-11
Research reviewed October 11, 2026. Published by the developer of ToSleep AI; not independently clinically reviewed. The cited researchers and institutions are not affiliated with ToSleep and do not endorse it.
The short answer: No. Dreams are often more vivid, emotional and story-like during REM sleep, but dream experiences also occur during non-REM sleep. A remembered dream is a report after awakening, not a direct sensor reading, and a watch cannot tell whether you were dreaming.
Do dreams only happen during REM sleep?
Dreaming can occur in both REM and non-REM sleep. REM became closely linked with dreaming because people awakened from REM frequently report vivid mental experiences. But laboratory awakenings also produce dream reports from NREM stages.
The National Heart, Lung, and Blood Institute explains that most dreaming occurs during REM and that some dreams can occur during non-REM sleep. NHLBI “Most” is not “only.”
Dream research also depends on recall. Researchers cannot directly observe the subjective story. They wake a participant and ask what, if anything, was being experienced immediately before awakening.
What is different about REM and NREM dreams?
REM dreams are often described as more vivid, emotional, bizarre or narratively complex. NREM reports can be shorter, more thought-like or closer to recent waking concerns, especially earlier in the night. These are tendencies, not rules.
| Feature | REM tendency | NREM tendency | Important limitation |
|---|---|---|---|
| Recall after awakening | Often more frequent | Still occurs | Awakening method changes recall |
| Content | Often vivid and story-like | Often more thought-like | Individual reports overlap |
| Muscle state | Major skeletal muscles normally relaxed | Muscle tone differs by stage | This does not reveal dream content |
| Brain activity | Distinct REM physiology | NREM slow waves and spindles | Dreaming cannot be reduced to one global stage label |
A stage label describes measurable physiology. A dream report describes remembered experience. They are related but not identical categories.
What did brain-recording studies find?
Dream reports in REM and NREM sleep share some local brain-activity patterns. A 2017 high-density EEG study compared awakenings followed by reports of dreaming with awakenings followed by no reported experience. In both REM and NREM sleep, dreaming was associated with less low-frequency activity in posterior cortical regions. Siclari et al., 2017
The researchers also found that higher-frequency activity in parts of this posterior “hot zone” related to particular content categories. Their real-time monitoring predicted whether participants would report a dream or no experience after NREM awakenings.
This does not mean researchers can watch a complete dream like a movie. It identifies statistical neural correlates under controlled conditions, and the result still depends on a participant’s report after being awakened.
How can dreaming happen during deep or NREM sleep?
NREM sleep is not a uniform period of total brain silence. Slow waves and sleep spindles vary across time and brain regions. Local patterns can differ even while the whole 30-second period receives one stage label.
A 2018 study recorded 14 healthy adults with high-density EEG and used repeated awakenings. NREM dream reports were preceded by fewer, smaller and shallower slow waves, plus faster spindles, particularly in central and posterior regions. Siclari et al., 2018
The study supports the idea that conscious experience during sleep relates to local activity, not just the broad REM-versus-NREM category. Its small laboratory sample does not provide a consumer method for detecting dreams at home.
Why do I remember some dreams but not others?
Dreaming and dream recall are separate problems. A mental experience may occur during sleep and leave no accessible memory after waking. Recall can depend on the sleep stage, brain activity before awakening, brief arousal, timing of the awakening and how quickly attention shifts afterward.
A 2022 state-of-the-art review emphasizes that dream science has indirect access to its subject: researchers generally rely on reports after awakening. Trait-like differences between people and state-like brain activity before a report both influence recall. Scarpelli et al., 2022
Not remembering a dream therefore does not prove that no dream occurred. Remembering several dreams does not prove that you spent unusually long in REM.
Does more REM mean more dreaming?
Not in a way a consumer graph can establish. More estimated REM creates more time in a stage strongly associated with vivid dream reports, but dream probability, content and recall vary within REM and NREM.
The graph also contains measurement error. A wrist device estimates stage from movement and pulse-related signals, while laboratory staging uses brain, eye and muscle signals. A 2025 meta-analysis of 24 studies and 798 participants found significant pooled differences between consumer wrist devices and polysomnography for several basic sleep measures, with performance varying by device. Lee et al., 2025
If the watch labels 90 minutes as REM, the defensible statement is “the algorithm estimated REM-like sleep,” not “I dreamed for 90 minutes.”
Can a sleep tracker detect nightmares?
A standard wrist sleep tracker cannot read dream content or diagnose a nightmare. It may record movement or heart-rate changes around an awakening, but those signals are not specific to fear, a particular image or a remembered dream.
Nightmares are defined through distressing dream experience and recall, not merely a pulse increase. Recurrent nightmares, dream-enactment behavior, injuries during sleep or major daytime distress deserve qualified clinical assessment rather than interpretation from a stage chart.
Is dreaming proof of good or bad sleep?
No. Dream recall is not a simple sleep-quality score. Vivid recall can follow a well-timed awakening from REM, but it can also accompany fragmented sleep or frequent awakenings. Little recall may reflect uninterrupted sleep, rapid forgetting or individual differences.
Avoid treating dreams as evidence that REM was “successful,” or no recall as evidence that REM was missing. Sleep duration, continuity, timing and daytime function are more useful dimensions to review.
How ToSleep handles REM estimates
ToSleep estimates awake, light, deep, REM or unknown intervals from Apple Watch wrist movement and available heart-rate signals. It does not measure EEG, eye movements, dream content or dream recall.
The REM color in ToSleep is an algorithmic sleep-stage estimate. It should not be used to confirm a dream, explain a nightmare or diagnose a REM-related disorder. If you want to track dreams, add a morning note in your own words and keep it separate from the stage estimate.
Learn how ToSleep works, how much REM sleep you need and how accurate wrist sleep trackers are.
Frequently asked questions
Can you dream in deep sleep?
Dream reports can occur from NREM sleep, including periods containing slow-wave activity. The experiences may differ from typical REM dreams, and recall depends on how and when the person is awakened.
Does every REM period contain a dream?
No study can verify every unreported subjective experience. REM awakenings often produce dream reports, but people sometimes report no recalled experience.
Why are morning dreams more vivid?
REM periods tend to become longer later in the night, and waking directly from a dream can improve recall. Later timing and recent awakening may both contribute.
Can Apple Watch tell when I dreamed?
No. Apple Watch and ToSleep can estimate a REM-like stage from wrist signals, but they cannot observe subjective dream experience or content.
Does remembering dreams mean I slept badly?
Not by itself. Recall may reflect awakening timing, individual memory and sleep fragmentation. Evaluate the broader sleep pattern and daytime functioning.
Sources
- Siclari et al. — The neural correlates of dreaming. Nature Neuroscience 20:872–878 (2017).
- Siclari et al. — Dreaming in NREM Sleep: A High-Density EEG Study of Slow Waves and Spindles. Journal of Neuroscience 38(43):9175–9185 (2018).
- Scarpelli et al. — What about dreams? State of the art and open questions. Journal of Sleep Research 31(4):e13609 (2022).
- NHLBI, NIH — Sleep Phases and Stages. Updated March 24, 2022.
- Lee et al. — Performance of consumer wrist-worn sleep tracking devices compared to polysomnography: a meta-analysis. Journal of Clinical Sleep Medicine 21(3):573–582 (2025).
Wellness information, not medical advice.