Also called sleep onset, Stage 1 non-REM sleep is the first stage of sleep that we slip into as we’re falling asleep, and is one of the three stages of non-REM sleep. This typically lasts for about ten minutes. Your eyes start to slowly roll around, your brain waves transition from the alpha waves you have while awake with your eyes closed, to slower, bigger theta waves.
In this stage of sleep you may experience hypnagogic hallucinations. The content of these kind of dreams varies widely, but in this stage of sleep you might expect abstract geometric patterns, flashes of colour, or contextless images. If you have been doing a repetitive task during the day, you might find that you see the image of it when you close your eyes to go to sleep. But you can also have more typically dreamlike experiences in this stage of sleep, with more complex, narrative episodes.
You are probably also familiar with the sudden jumping sensation that can occur in this stage of sleep: this is called the hypnic jerk, and is often accompanied by a dream experience of suddenly falling. Although it’s not known for certain why this happens, it’s most likely to do with the relaxing of the muscles as we slip into sleep, which the brain may misinterpret as falling over, so it sends signals to them to jump back into action.
To see where in the night this stage of sleep occurs, take a look at a typical hypnogram. The fantastic diagram below from the website HumanPhysiology.Academy illustrates what our brainwaves look like in the different stages of sleep.