The Australian reports on the different stages of sleep.

Sydney-based psychologist and wellness specialist Harriet Sciberras, who teaches sleep-better seminars, says each sleep cycle is divided into five stages: pre-sleep; light sleep; deep sleep (in two ­stages); and rapid eye movement sleep. Cycles take about 90 minutes to complete, meaning we cycle through roughly five rotations a night. But the amount of time spent in each stage of sleep varies within each cycle, with more deep sleep happening earlier in the night, more dreaming sleep in the second half of the night.