No. 24: Nov-Dec 1982
Many curious mental states occur during sleep, most of which we cannot begin to explain. Horne homes in on REM sleep (Rapid Eye Movements sleep), during which:
(1) Both heart and respiration rates become irregular; (2) The flow of blood to the brain increases 50% over relaxed waking levels; (3) Body temperature regulation becomes impaired; and (4) Blood flow to the kidneys and urine production drop markedly.
REM sleep is thought to be "primitive" from an evolutionary standpoint because body temperature control is "reptilian." Horne also discusses REM and normal sleep in the context of nightmares, sleeptalking, sleepwalking, night terrors, narcolepsy, and sleep paralysis.
(Horne, Jim; "The Cinema of the Mind," New Scientist, 95:627, 1982.)
Comment. All in all, sleep is a complex phenomenon. We know we need it, but why? A really efficient organism would run 24 hours a day -- like a computer.