1) Sleep occurs in cycles with non-REM and REM periods. During non-REM sleep our muscles relax through four stages, while REM sleep involves dreaming and eye movement but paralysis of muscles. 2) Lack of sleep has serious cognitive and physical effects like decreased concentration, impaired memory, and increased stress and blood pressure. 3) While the exact sleep needs vary, adults generally require 7-9 hours of sleep per night, with animals' sleep ranging from 1.9 hours for giraffes to 18 hours for pythons.