Sleep cycles last for about 90 minutes. You should aim to wake up between them, and not in the middle.
More about sleep cycles:
When you sleep, you go through several sleep cycles. They last around 90 minutes and you need 4-6 of them to get completely restored.
During one sleep cycle, you go through different stages of sleep. This can be seen in a hypnogram:
N1: The lightest sleep stage. Here you are half awake and half asleep. People often think they didn’t sleep if they wake up from this stage.
N2: Still pretty light, but here you are unconcious and on your way to the deeper stages of your sleep.
N3: Deep sleep. Also called slow wave sleep, this is the stage where a lot of important recovery processes happen, such as the glymphatic system.
R (or REM): Dreaming. The REM (rapid eye movement) stage is the stage where you are dreaming, this stage is important for memory consolidation and cognitive functions.
Waking up in the middle of a sleep cycle, can make you feel groggy and tired. If you wake up between cycles, you’ll feel more refreshed and alert.
Length of sleep cycles
The length of sleep cycles varies from 70 to 100 minutes. They might also vary in length throughout the night (we are not machines after all).
Young children can have shorter sleep cycles, as low as 60 minutes.
Waking up without an alarm
In an ideal world, you would wake up without the use of an alarm. Automatically you would wake up in the lightest of the sleep stages – not in the middle of a sleep cycle.
Waking up without an alarm can be a good way to determine your sleep cycle length.
If you wake up in the middle of the night, it is also often in between cycles.
Don’t overthink it
This tool is meant as a guide to how you can plan and understand your sleep. However, some people can get overly obsessed with it.
See your bed as your safe place to rest and recover. If you can’t sleep, don’t catastrophize it. Get out of bed or do something else for a while. Many people don’t need as much sleep as everyone else anyways.