What Counts as a Sleep Cycle
Sleep is not uniform. A night divides into cycles of roughly ninety minutes, each moving from light sleep into deep sleep and then into REM. Deep sleep dominates the early cycles and REM the later ones, which is why cutting the last two hours removes most of the REM rather than a fifth of everything.
That asymmetry is the fact worth teaching, because it changes what a shortened night costs. A student who sleeps five hours has not lost a proportional slice of rest; they have lost the specific stage most involved in consolidating what they studied. What should never reach the published cut is any clinical territory: sleep disorders, medication, and anything resembling individual advice belong with a health professional rather than in a lesson video.
The template breaks the night into six scenes: one on the cycle structure and its length, two on what happens in deep sleep and REM, one on how the balance shifts across the night, one on what a short night actually removes, and one on the habits that protect the later cycles.
