Before I get into the meat and potatoes, I think it will be of some benefit to get an overview and an understanding of the sleep cycle and what the brain does and how the body and mind responds needs to be explained through the eyes of science. The only thing that science has not measured is what takes place in the mind. We need to recognize that the scientific community still has not come up with a proven hypothesis of the existence of the mind. It is still a subject of debate that the mind and brain are one, or that the mind is separate nonphysical aspect of our existence. I have taken the position of the latter. I have taken this position because of my experiences.
When we lay our heads down to sleep a five stage process takes place. In addition to the five stages a process also takes place within our brains and body.
During the time when we are awake living and doing our conscience daily activities the brain waves are operating at a frequency of 14-30 hertz. It is called the Beta state.

Sleep cycles & Brain wave activities uncovered

Stage 1: This is the stage is called pre-sleep. This stage usually lasts for 10-15 minutes (time factor is not written in stone). Some people may experience sudden muscle contractions or jerking of the limbs. Then preceding the limb movement one may have the sensation of falling. During this stage the brain waves will slow down between 8-12.9 hertz.
When the brainwaves slow down to 8-12.9 hertz, it is called the alpha state. The mind and body start to respond when the brain waves are in the alpha state. The body starts to produce neuro chemicals that give us a feeling of relaxation. Then the mind starts the process of introspection. This is the process when we begin to examine our own thoughts and feelings. The alpha state is predominate brain wave pattern during meditation. It should be noted that the alpha state can occur during moments when we are not sleeping. For example one may be absorbed and focusing their attention in reading a book or some other activity. This is when our ability to learn becomes enhanced.
In essence while the beta state deals with the external. The alpha state allows us to deal with the internal opening doors for introspection, relaxation, learning, meditation, the feelings of inner peace and contentment.

Stage 2: This stage lasts for about 20 minutes for most people. This is the period when the onset of sleep occurs. You are not quite asleep yet. During this period the brain waves starts to slow down even further. The brain waves fall down between the frequencies of 4-7.9 hertz. When the brainwaves reach these frequencies it is called the theta state. During the theta state the body temperature and heart rate starts to decrease. At this stage the body begins to work to heal itself. Also the mind becomes active.
It is during the theta state that the mind is in between the conscious and unconscious. We retain the memory and feelings of the information that the unconscious reveals. We are connected with our creativity. We may have subjective experiences that have been characterized with feelings of inspiration and can be spiritual. It is also said the psychic phoneme occurs at this state. We may have a sense of receiving information of events and feelings that may have taken place, or information of events and feelings that will take place.

Stage 3: This stage is the transitional phase between light and deep sleep. No subjective experience happens at this stage. The brain waves begins to slow down it frequencies to .1-3.9 hertz. When the brain wave reaches those frequencies it is called the delta state. However, the delta state isn’t dominant at this stage.

Stage 4: During this stage the delta state becomes dominate. This is the stage of normal sleep. For most people this stage last for about 20 minutes. Usually there is no subjective experience taking place, and dreams may not occur.
Some have postulate that the mind makes contact in what is described humanity’s collective consciousness. Some feel some type of unity with humanity. Also it is recognized that even though the body may be sleeping. The mind can still be awake. Hench there is an awareness of your surroundings and you may even see the room if the mind remains awake.
Stage 5 REM (rapid eye movement): This is called the normal dream state. This stage is characterized by the movement of the eyes. In this stage while the brain and mind is very active, the body paralyzes itself. This state of paralysis prevents the voluntary movements of the limbs. It is a protective measure to ensure that you do not act out when you are dreaming. REM also takes place during deep sleep. When you dream you will see images, and feel full emotions. Most people do not retain memories of their dreams.

It takes 90 minutes for the full cycle occurs. Keep in mind that sometimes we do not experience the REM. The cycle may not always take place in sequence. For example the cycle will start off with stage 1 and go through to stage 4. After stage 4 REM may occur then we will revert to stage 2 and may hoover between stages 3 and 4. It should be noted that stage 5 may last up to one hour. However, how long a dream last is really according to our mind’s perception.