In short, it is a survival mechanism.
According to the American Sleep Association, sleep is when
our body repairs and replenishes itself even when we don't feel it. Just as we run on different time zones, our body
has its internal clocks (circadian rhythm) For example, growth hormone goes to work and spikes during our
sleep!
Non Rapid Eye Movement (NREM 1)
These are the initial 5-10 minutes when we tether between falling asleep and being awake. For some, it may not even
feel like sleeping! Since sleep stages are named after eye movements, the initial 3 stages are similar in that
regard but not entirely!
NREM 2
This stage typically lasts for ~20 minutes. Here, body temperature, heart rate, and breathing gradually slows
down. Despite only lasting 20 minutes, one spends most of an entire night’s sleep here
NREM 3
This stage commences deep sleep. One becomes unresponsive to the environment and muscles are the most relaxed, it is
very hard to wake someone from this stage.
Rapid Eye Movement (REM)
Dream on! This is when dreaming occurs and when our muscles and brain become polar opposites - very relaxed and very
active respectively. Not only does our eyes move rapidly, our respiration and heart rates increase, too! As much as
our dreams may seem to last forever, this stage only takes up ~20% of our total sleep!