Short answers, pulled from the story.
Sleep divides into non-rapid eye movement sleep and rapid eye movement sleep. Non-REM arrives first and deepens into slow-wave sleep, while REM, also called paradoxical sleep, brings fast brain waves, eye movements, near-paralysis, and most dreams. The American Academy of Sleep Medicine splits non-REM into three stages, N1, N2, and N3.
A full cycle of alternating NREM and REM sleep averages about 90 minutes. It repeats four to six times in a good night's sleep, normally running N1 to N2 to N3 back to N2 and then into REM. Deep N3 sleep dominates early in the night, while REM increases in the cycles just before natural awakening.
Early in 2015 the National Sleep Foundation in the US recommended 14 to 17 hours for newborns aged 0 to 3 months and 12 to 15 hours for infants. The figures decline with age to 7 to 9 hours for adults aged 18 to 64 and 7 to 8 hours for older adults aged 65 and over. Newborns may need up to 18 hours a day.
During sleep the glymphatic system clears metabolic waste from the brain faster than during waking by increasing the flow of cerebrospinal fluid, removing metabolites including amyloid. The body can run restorative processes during quiet waking, but the brain actually requires sleep, which is why one researcher called sleep of the brain, by the brain and for the brain.
Caffeine in coffee, tea, and other sources temporarily blocks adenosine, a neurotransmitter that builds up during wakefulness and signals sleep debt. By blocking it, caffeine prolongs sleep latency and reduces total sleep time and quality. High amounts can interrupt sleep patterns and lead to a cycle of drowsiness and more caffeine use.
The earliest is the Greek legend of Epimenides of Knossos, who the biographer Diogenes Laertius said fell asleep in a cave under Mount Ida and woke fifty-seven years later. The Christian legend of the Seven Sleepers of Ephesus has them waking 360 years later. Washington Irving's Rip Van Winkle, first published in 1819, sleeps twenty years through the American Revolution.