• Circadian rhythm: a 24-hour internal clock that cycles between sleepiness and alertness at regular intervals (your sleep/wake cycle) and is regulated by hormones and light.
• Melatonin: a hormone that your brain produces in response to darkness, which helps with the timing of your circadian rhythm and sleep.
• REM latency: the time between when you fall asleep and enter REM sleep.
• REM sleep: a cycle of sleep with rapid eye movements that involves more dreaming and body movement, faster pulse and breathing. REM sleep makes up 25 per cent of an adult sleep cycle and benefits learning, memory and mood.
• Sleep efficiency: the total time in bed vs time spent sleeping.
• Sleep hygiene: a variety of practices, techniques and tools that improve the quality of your sleep.
• Sleep latency: how long it takes after your head hits the pillow to fall asleep.