All sleep is not the same. Each night your body and mind go through 4 to 6 sleep cycles with up to 4 sleep stages/phases each.

A sleep cycle is defined as the time between you being awake or almost awake, with phases of deeper sleep in between. A sleep cycle typically lasts around 90 minutes.

Sleep stages (or phases) usually have a duration of between a few minutes and 30 minutes and are distinguished by a number of measurable characteristics.

Sleep researchers define the following sleep stages: REM (Dreams), NREM 1 (Light Sleep), NREM 2 (Medium Sleep), NREM 3 (Deep Sleep).

Rapid eye movement (REM) sleep features intense dreams. Often these dreams relate to experiences of the previous day. Your brain secretes neurotransmitter chemicals that temporarily “cut” the connection between nerves and muscles and so paralyze your muscles, to prevent injuries from living out these dreams. REM sleep helps with learning procedural tasks, while NREM 3 sleep (see below) is responsible for declarative memory consolidation, i.e. learning things like vocabulary, math, etc. Usually you first enter REM sleep at the end of the first sleep cycle, around 90 minutes after first falling asleep.

The Non-REM 1 (NREM 1) sleep phase is the transition between wakefulness and sleep. It’s also called light sleep. Your breathing slows, your muscles relax as body and mind prepare for deeper sleep.

Eye movement stops in the NREM 2 phase. This sleep phase is also called medium sleep. Your heartbeat and breathing slow further. Brain activity, as measured by electroencephalography, slows, interrupted by short burst of fast brainwaves. Brainwaves are electrical (and very small) voltage fluctuations measurable by sensors in a lab. They are caused by the actions of billions of neurons in the cerebral cortex - the outer layers of the brain responsible for reasoning, sensing and motor skills.

NREM 3, also called deep sleep, is your deepest sleep phase and is the most important for physical and mental regeneration. Your musculoskeletal system is at its most relaxed, your heartbeat is at its slowest, as are your brain waves. Breathing is very slow and very deep. It is very difficult to take up a person who is in NREM 3 sleep.

Recent research has shown that NREM 3 is the most crucial sleep phase for learning and memory consolidation as well as physical repair and growth, including recuperation of the immune system. The immune system doesn’t just safeguard you from viruses and bacteria, but is also able to kill cancer cells, protecting you from cancer.

NREM 3 sleep also has special importance for cleaning up neurons in the brain, including removing harmful (mis-folded) proteins that in the long run can lead to Alzheimer’s disease.

Sleep research studies have shown that once they are able to properly sleep, sleep deprived people spend a larger than normal amount of time in NREM 3 sleep. This underlines the special importance of NREM 3 sleep for physical and mental recuperation.

Sleep research studies on human subjects have shown that continuous gentle side to side movement of their bed shortens the time it takes to reach NREM 3 and increases the time humans spend in NREM 3 deep sleep. This enhances the overall quality of sleep and improves their ability to learn.

As the night progresses each successive sleep cycle becomes shallower, with less time spent in deep NREM 3 sleep and more time spent in medium, lights and REM sleep. Gentle side to side movement of your bed helps you to maintain deep NREM 3 sleep longer and hence wake up fresher and with better formed memory of things learned previously.