Stage 1
This is the beginning of the sleep cycle and is a relatively light stage. This is more of a transition period between wakefulness and sleep. In Stage 1, the brain produces high amplitude theta waves, which are very slow brain waves. This period of sleep lasts only a brief time (around 5-10 minutes).
Stage 2
This stage lasts for approximately 20 minutes. The brain will begin to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. Your body temperature starts to decrease and heart rate begins to slow.
Stage 3
This is deep, slow brain waves known as delta waves begin to emerge during stage 3 sleep. Stage 3 is a transitional period between light sleep and a very deep sleep.
Stage 4
At this stage, sometimes referred to as delta sleep because of the slow brain waves. This is a deep sleep that last for approximately 30 mins.
Dreaming

A majority of the dreaming occurs during the stage referred to as REM, or the rapid eye movement stage. This is characterized by eye movement, in which the eyes dart back and forth under the eye lids. Dreaming occurs during this stage because of increased brain activity, voluntary muscles become paralyzed.

There are five common beliefs about dreaming. They are: External stimuli are incorporated in to our dreams. Dreams last only an instant. They do not dream. Penile erections indicate sexual content of dreams. Sleep talking/walking can occur.

Two common theories that have been considered are Freud’s. Which concentrates on sexual desires and symbolism and Jung’s who felt our dreams reflect on our waking selves and solve our problems or think through issues.

Personally, I lean more towards Jung’s theory. However, I also view dreams as messages sometimes. When I have a dream that seems to stay on my mind for a day or two, there is usually a message that I will finally realize, that came to me in my dream.