Sleep is vital to every mammal, bird, reptile, amphibian and
fish on the planet. Scientists have explored the question of why we sleep from
many different angles. Various reasons thought of are:
1 - Sleep enables the body to rest; in contrast to the
highly active anabolic state that dominates during waking hours. It helps
replenish fuel, which is burned while awake
2 - The primary function of sleep is to reduce an
individual’s energy demand and expenditure
3 - During sleep, the body has a chance to clear adenosine
(which is responsible for feeling of tiredness) from the system, and, as a
result, we feel more alert when we wake up.
4 - Humans sleep to dream. Dreams allow the mind to file
away important memories (including new skills) and discard unwanted information
at the end of a busy day. Sleep might also be a time for your brain to do a
little housekeeping.
5 - Inactivity at
night is an adaptation that served a survival function by keeping organisms out
of harm’s way at times when they would be particularly vulnerable.
6 - Sleeping protects all animals from attack during the
night, because they sleep in a safe, dark place out of reach from predators.
7- Sleep helps the body to heal, by dedicating energy to
repairing the immune and nervous systems
The real reason for sleep could be any combination of
these ideas :)