Sleep is divided into different phases of light and deep sleep throughout the night, occurring in cycles of approximately 90 minutes each. Each 90-minute cycle includes periods of non-REM sleep and REM (rapid eye movement) sleep, which is when our brains are more active, and dreams often occur.

Sleep cycles change throughout life stages and can be affected by a number of things, such as disruption to your body clock (circadian rhythms), daytime napping, stress, exercise or too much exposure to light before bedtime, particularly blue light.