Sleep & dreams.

A night consists of several cycles of about 90 minutes each. In every cycle we move through light sleep, deep sleep, and a REM (Rapid Eye Movement) phase. As the night progresses, REM phases get longer.

Most vivid dreams occur during REM sleep. The brain is almost as active as when awake, while the skeletal muscles are largely paralysed — presumably so we don't act dreams out.

Dream content also occurs outside REM sleep, but is usually less vivid and harder to remember.

Research discusses several functions without a single definitive answer. Plausible candidates include:

• Memory consolidation — experiences are sorted and integrated into existing knowledge.
• Emotion regulation — distressing impressions often lose their edge overnight.
• Creative linking — the brain combines content in unusual ways, which can shed new light on problems.
• Threat simulation — an evolutionary hypothesis: dreams 'rehearse' emergencies.

Dreams are not 'meaningless' — but they are also not encoded messages from another world. They are an honest by-product of the brain's nightly work. Recording and contextualising them helps you get to know yourself better.