Our brain has four rhythms of emission :
1.Rhythm Bêta: Brain emits a rhythm between 12 and 40 cycles
per second during a full consciousness,for example during you are walking ,
reading ,watching TV,or working.
2.Rhythm Alpha is between 7 and 12 cycles per second:It`s the first level
of meditation for example you are taking a rest ,you are lying down on
your couch and you are starting to dream without falling asleep.You are in
that alpha : It`s easy to reach this level involuntarily.Another example:
when you are getting bored during an audience.
3.Rhythm Thêta is between 4 to 7 cycles per second .That the first level
of deep sleep.When we are in this rhythm,we almost feel nothing our body.
But we can be conscious of our body.It`s the last level before unconsciousness
4.Rhythm Delta is the emission of the brain between 1 and 4 cycles,
It`s the extremely deep sleep.It`s the level of unconsciousness!
The searchers have shown that The rhythm Delta lasts for about
45 minutes each night when we sleep.In this extreme deep sleep,
we recover(get) most energy of the rest(relax)If you sleep in Delta
for 20 minutes,you will wake up tired.If you sleep in Delta for
2 hours each night,you will wake up full of strength (energy).
The text above is from the book written in French by Patrick Drouot,
an American Author of the book : Nous sommes tous immortels.
(I translated it at page 130 into English)