We all know the importance of good sleep for development and healthy bodily function but how many of us realise what is actually going on each night when we jump into bed – it’s not just a case of shut your eyes and off you go. Many may be familiar with the term sleep cycle but what does it actually mean?
Sleep consists of 5 stages that repeat themselves throughout the night. A cycle takes approximately 90 – 120 minutes to complete, moving from Non REM (Rapid Eye Movement) Stages 1 through Stage 4 then into REM sleep before starting again. While each stage is quite different, all are of equal importance.
Stage 1- a relatively short stage, usually lasting less than ten minutes. Here your body relaxes and your breathing and heart rate slow. Drifting between wakefulness and sleep, you may still be aware of your surroundings but will be slow to respond.
Stage 2 – approximately 50% of your sleep time is spent here. With the onset of sleep your brain activity (measured in waves) slows, further lowering your levels of consciousness. As you slip deeper into sleep short spurts of wave activity pepper your brain, cushioning your awareness from your surroundings and allowing you to remain asleep.
Stages 3 & 4 – known collectively as the ‘deep sleep’ stage and characterised by Delta waves, extremely slow brain activity, you will be totally relaxed and difficult to wake. Here with a low heart rate, blood pressure and body temperature, blood flow increases to your muscles and essential hormones are released. Your body experiences its most restorative sleep, essential for any growth or repair.
REM Sleep – this last stage in the sleep cycle accounts for nearly a quarter of your sleep time and is characterised by rapid and erratic eye movements and an increase in physiological function. Muscles become paralysed in REM sleep and vivid dreams are prevalent. Researchers believe that this stage of sleep aids your ability to decode life experiences and to make sense of the world.
Each night these stages are repeated several times. As the night progresses, each cycle contains more REM sleep and less deep sleep, with the length of REM periods increasing each cycle. By morning sleep is mostly stages one and two, with possibly an hour of REM sleep.