Thank you for your question.
What is sleep and why do we do it?
"No one knows for sure why we sleep, but here are 2 basic theories:
1. Sleep has a restorative function.
2. Sleep has an adaptive function.
Sleep as a Restorative Process
"This theory of sleep suggests that sleep helps the body recover from
all the work it did while an animal was awake. Experiments have shown
that the more physical exercise an animal does, the more SWS an animal
will have. Also, if people are deprived of SWS by waking them up each
time they get to stage 4 sleep, then they complain of being physically
tired. If people are deprived of REM sleep by waking them up each time
the have REM type EEG patterns, they can get anxious and irritable. If
animals are deprived of REM for several days and then allowed to get
an undisturbed period of sleep, animals will go into "REM rebound" -
this is when REM periods of sleep will happen more often and for a
longer time than normal.
Sleep, especially REM sleep, has also been thought to be important for
memory and learning. It is possible that sleep helps form memories.
Sleep as an Adaptive Process
Sleep may have developed because of a need of animals to protect
themselves. For example, some animals search for food and water during
the day because it is easier to see when the sun is out. When it is
dark, it is best for these animals to save energy, avoid getting
eaten, and avoid falling off a cliff that they cannot see. It is
interesting to note which animals sleep the most and which sleep the
least. In general, animals that serve as food for other animals sleep
The Straight Dope - Why do we sleep?
Why do we sleep?
librarythinkquest.org - Why do we have to sleep?
human need to sleep
why we have to sleep
sleep as a restorative process
sleep as an adaptive process