What Happens When We Sleep?

Many years of research, scientists still aren't entirely sure why do we sleep.
And it is common to all living beings in this evolution.
when it comes to scientific reason, sleep can be divided into 2 levels.
Rapid eye movement and Non-rapid eye movement.

REM sleep is unclear cause during night we have our vivid dreams,

NREM nearly 72-80% of electrical patterns in our brain called "sleep spindles" and high, slow delta waves force us to slip into deep sleep.

Difference between REM & NREM is very simple
NREM sleep.                         REM sleep.
Dreams tend to be                 Dreams are more vivid & emotional
more concept- based

Level 1. 1-8 minutes
Our eyelids are heavy and head starts to drop during drowsy period and the brain is still active.

Level 2.  11- 26 minutes
Second phase of sleep, our eyes stops moving, easily woken. brain activity slows further.

Level 3.  approx 28 minutes
In this time, entered into moderate sleep and then slowly into deep sleep, at this level difficult to wake up cause our brain produces triangle waves with occasional spikes.

Level 4.  above 35 min
This is the deepest level during this time, extremely hard to wake up.
our muscle relax with delta waves and breathing becomes slow & rhythmic, that can route to snoring.

Level 5.    after 50 minutes
In this level our brain shows too much of intreast in deep sleep.
our muscle are temporarily paralysed, when electrical activity starts, at this time most dreams happen.
our eyes fire back and forth this point is rapid eye movement.

Thanks to Google