Sleep is not one steady state. Through the night you move through repeating cycles of lighter sleep, deep sleep and REM sleep, each lasting roughly 90 minutes.
Light Sleep
Light sleep makes up a large part of the night and acts as a transition between stages.
Deep Sleep
Deep sleep tends to be concentrated earlier in the night and is associated with physical recovery.
REM Sleep
REM sleep, when most vivid dreaming happens, tends to increase later in the night and is linked with memory and emotional processing.
Practice
For one week, keep a simple sleep diary: bedtime, estimated time to fall asleep, wake time and how rested you feel from one to five.
Key Takeaways
The three ideas to carry forward from this lesson are: light sleep, deep sleep and REM sleep. You do not need to master all of them at once. Pick the one that feels most relevant to your situation right now and apply it before the next lesson.
Quick Reflection
Ask yourself where the ideas in Sleep Cycles already show up in your own life or work, and where they are missing. Write down one example of each. Naming a real example makes the lesson concrete and shows you exactly where to apply it first.
How This Connects
This lesson is part of the How Sleep Works module. The next lesson, Sleep Need and Sleep Debt, builds directly on what you have just practised, so keep your notes from this exercise close by. If something here felt unclear, re-read the section that tripped you up before moving forward rather than pushing on.
Before You Move On
Before you move on, write two or three lines in your notes: what you tried, what felt awkward and what you would repeat. Those short notes turn Sleep Optimization & Recovery Science from something you read into something you practise, and they give you a record to compare against when you reach the final module.
This is educational content only and is not medical or clinical advice, diagnosis or treatment.