Non REM & REM Sleep Cycles

What's the difference between Non REM and REM Sleep?

Human beings have two cycles of sleep, Non REM and REM that alternate throughout the night in 90 minute periods. 

In simplistic terms, the function of Non REM is like defragging a computer or tidying a cluttered desk after a busy day.  All the paperwork on the desk that is of importance is put in the in-tray (moved from short-term to long-term memory), while anything deemed irrelevant (i.e. of no interest to you) is discarded and forgotten.  A lack of Non REM sleep often causes anxiety because the mind has not been sorted at the end of each day.

REM sleep is about integrating recent experiences with past experiences to build a greater, inter-related understanding of the world.  Signals of emotions, motivations and memories are played out on the screen of our mind to help us evaluate and come to terms with thoughts.

Interestingly, in REM sleep, some parts of our brain are more active than when we are awake, while our body is simultaneously paralysed to prevent us enacting our dreams and harming ourselves.

REM is for the integration of new with old and, as a by-product, fuels creativity, helps us problem solve (“sleeping on it”), make better decisions, take an overview of a mass of information and resolve anxious making problems. 

Musicians will often find they play a new piece of music better in the morning than they did when practising the night before, simply because the REM has allowed the musician to apply the benefit of past experience.

There is a predominance of Non REM at the beginning of the night and a shift to more REM as the night goes on.  It is thought that the processing done in REM throws up more material and hence why there are periods of Non REM later on, to provide a secondary sorting process.

As we pass through life, the quantity of each type of sleep changes.  Pre-birth babies initially spend most of their time in a state similar to REM and then through life, this mixes to varying degrees with Non REM.  In the later stages of life, Non REM decreases which helps explain why many older people notice their memory weakening.


Severn Sleep is the first dedicated CBTi sleep clinic in Shropshire, Powys and Worcestershire. Appointments are available at our clinics in Brecon, Ludlow, Shrewsbury and Malvern. Alternatively, we offer appointments via Skype to clients across the UK and rest of the world.

Please Call Severn Sleep on: 07799 625628