← 🫀 Human body · usually met in Std 6-12
Not switched-off time. The brain is busy during sleep consolidating memory and clearing waste, and losing it costs you more than feeling tired.
Sleep runs in cycles of roughly ninety minutes, alternating deep slow-wave sleep with REM sleep, when most vivid dreaming happens. Deep sleep appears to matter most for physical recovery and for moving the day's learning into longer-term memory; REM is associated with emotional processing. Both are needed, and they are not interchangeable.
For a student, the practical point is simple and well supported: material studied and then slept on is remembered better than material crammed through the night. Screens late at night delay the body clock, because light — especially bright and blue-heavy light — tells the brain it is still day. Teenagers' body clocks genuinely run later than adults', which is biology rather than laziness, but it does not remove the need for the hours themselves.
Want to see it moving? Search YouTube for “Sleep” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.
This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.
Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus. World Health Organization ↗Health facts stated carefully, and updated when the evidence changes.Last gone through: 1 October 2026 · How these entries are written
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