There are five stages of sleep. Stages one and two are light sleep, three and four consists of deep sleep, and five is called the REM (Rapid Eye Movement) or dreaming phase. We enter early sleep, Stage 1 when our melatonin levels have risen.
Stage 1 usually lasts a few minutes. Stage 2 makes up a bulk of our night's sleep, around 50%. During deep sleep (Stages 3 and 4) our body and mind repair and rebalance. It is during this time that our stress hormones reduce, our energy stores are replenished, our muscles and tissues heal, growth hormone is produced, detoxification occurs, and our emotions are processed.
A large proportion of healing occurs during the first part of our deep sleep early in the night. Ideally, this first phase of sleep should occur before midnight as it is a vital component that can affect the quality of sleep. By working late into the night, or using electronic devices before bed, it sets back this essential process occurring.
Stage 5 (REM) sleep is the shortest during the first cycle of sleep, lasting typically under 10 minutes, and lengthens through your sleep to approximately 45 minutes in the early hours. It is also an important part of your sleep and is when your brain is extremely active. It is during this stage that the parts of our brains involved in learning are stimulated. It helps to process the information we have gathered throughout the day.
The more you stimulate your mind just before sleep, the more REM sleep will be required to sort out this information, and the less deep and restful sleep will be attained. This can leave you feeling overtired in the morning as if you have been overworked all night with all that excess mental energy.
The pattern of these stages will differ from night to night and person to person. It is also age dependent, for example, sleep often becomes lighter with age.