Why do we need to sleep?
Sleep is not an optional extra in life; it is a fundamental requirement. In fact, you could survive for three times as long without food as you could without sleep. Much of what we know about the importance of sleep comes from experiences of people who have taken part in sleep-deprivation experiments. That is, where insufficient sleep, or no sleep, has been taken over successive 24-hour periods. The bottom line is that when people are sleep deprived they are not able to function properly during the day. So, one simple answer to the question “What is sleep for?” would be that the purpose of sleep is to make sure of good-quality daytime functioning.
Sleep has its physical, mental and emotional processing components, so when we have had no sleep, or insufficient sleep, these processes are not able to do their work so effectively. In physical terms we will feel lethargic and sleepy, mentally we become slowed down with poorer concentration and memory, and emotionally we may become irritable and rather down, though sometimes with excitable bursts of hyperactivity too.