Inside us
Sleep
You switch off the light. Your brain does not simply switch off.
Sleep cycles through non-REM and REM stages. Brain activity changes across the night rather than stopping.
A closer look
The picture, in three parts.
Settle
You move into non-REM sleep.
Cycle
Non-REM and REM stages recur through the night.
Dream
Changing brain activity can include vivid experiences.
Where could this take you next?
Sources & further reading +
Short explanations, grounded in published sources. Follow the originals for depth and context.
Sources checked: 10 September 2026. Visuals are illustrations, not documentary evidence.
Our approach to sources and corrections