During sleep the brain cycles through light, deep and REM stages. Sleep supports memory, mood, immune function and tissue repair.
How it works, step by step
Light sleep: heart rate and temperature drop.
Deep (slow-wave) sleep: growth hormone release peaks; body repair.
REM sleep: vivid dreams; important for memory and emotional processing.
Cycles repeat roughly every 90 minutes through the night.
How much
Adults generally need 7 or more hours per night; teenagers 8–10 hours.
Practical
Consistent sleep and wake times, daylight in the morning, and a dark, cool room are well-supported habits.
When to get help
Loud snoring with pauses in breathing, or daytime sleepiness that affects safety, is worth discussing with a clinician.
Evidence & sources
Adults should sleep 7 or more hours per night on a regular basis. Evidence: strong. Known: Consensus of sleep experts after systematic review of evidence linking short sleep with poorer health outcomes. Unknown: Optimal amounts vary between people. Source: American Academy of Sleep Medicine & Sleep Research Society, Recommended Amount of Sleep for a Healthy Adult (joint consensus statement) (2015).