Sleep is neither just the absence of wakefulness nor it is an inactive process...You are asleep for one third of your life and it is not just a little respite from wakefulness. It is a very complex and at the same time a very ordered process.
Sleep is made up of different stages which occur in orderly cycles throughout the night. Each stage of sleep has specific functions and we spend a certain amount of time in each of these stages. Any variation or interruption to this orderly fashion or organised pattern can affect sleep quality and in turn daytime functioning.
Why do we sleep?
Just like food and exercise, sleep is a fundamental requirement. Our muscles recover and repair during sleep; our memories are organised during sleep. Infants and children need so much sleep because they are growing. Lack of sleep in adults can lead to inability to focus,memory problems, fatigue, drowsiness and inability remain awake during the day. It is also important for our emotional wellbeing. It is common to feel irritable, overly anxious and even depressed after poor sleeep.
What controls our sleep?
There are two processes that control our sleep. One is our 'drive' for sleep (homesotatic sleep drive) and the second process controls 'when' we sleep (circaidan rhythm sleep drive).
Our sleep drive is managed by a 'sleep economy'. For every hour we stay awake, we accumulate a 'sleep debt' which is paid off in full by sleeping through the night. But if you don't sleep through the night or if you don't sleep enough, you develop a chronic sleep debt as you see in insomnia. The more the debt, the less likely you are to function normally during the day.
The sleep-wake schedule is managed by the circadian rhythm or the body clock. The hormone melatonin is responsible for the regulation of the body clock and promoting sleep. Its production rate is dictated by natural light; during hours of darkness melatonin is produced and sleep is promoted. Melatonin production is shutdown in the morning when there is natural light and wakefulness is promoted.
When these two prcoesses are in harmony, there is reduced tendency to sleep during wakeful hours and good sleep ensues during dark hours.