There are two types of sleep- Non REM and REM sleep and there are 4 stages of sleep which we cycle through several times throughout the night.
1.NREM stage 1- this is essentially dozing off and usually lasts around 5 or 10 minutes. The body hasn’t fully relaxed in this stage though the brain starts to slow down and there may be brief movements or twitches. It is easy to wake someone up from this stage of sleep.
2.NREM stage2- our bodies really start to relax and our temperature starts to drop, our heart rate and breathing slow down. This stage lasts for 10-25 minutes but each stage 2 that you experience through the night becomes progressively longer.
3.NREM stage 3- this is deep sleep and it is thought that this type of sleep is the most restorative and important sleep stage. It is when our brains remove waste and our cells repair themselves. We spend most of the time in deep sleep in the first half of the night and it is difficult to wake someone from this sleep stage. If they are woken there may be a period of disorientation lasting up to half an hour after waking. Each stage 3 lasts around 20-40 minutes but gets shorter though the night and more time is spent in REM sleep instead.
REM sleep- during REM sleep brain activity actually increases but our muscles are paralysed with the exception of the eye and breathing muscles. This is the stage of sleep when we have the most vivid dreams and REM sleep is thought to be essential for cognition, memory and learning. It is when our brains re-energize! You don’t enter REM sleep until you have been asleep for around an hour and a half and the REM stages get longer through the night- the first REM sleep stage may only last a few minutes.