The Sleep Cycle

One sleep cycle comprises of four stages and last for about 90-120 minutes. There are some texts that list five stages in the sleep cycle. Some consider the first five-ten minutes when you are falling asleep as a stage in the sleep cycle. We feel this is more of a transitional phase. In addition, while the other stages of sleep repeat themselves throughout the night, this phase of sleep does not. For this reason, we have excluded it as part of the sleep cycle.

Dreams can occur in any of the four stages of sleep but the most vivid and memorable dreams occur in the last stage of sleep (also commonly referred to as REM sleep). The sleep cycle repeats itself about an average of four to five times per night, but may repeat as many as seven times. Thus, you can see how a person has several different dreams in one night. Most people, however, only remember dreams that occur closer toward the morning when they are about to wake up. But just because you can't remember those dreams does not mean that they never happened. Some people swear on the fact that they simply do not dream when in reality, they just don't remember their dreams.

The Stages Of Sleep

The stages in the sleep cycle are organized by the changes in specific brain activity.

Stage 1: You are entering into light sleep. This stage is characterized by Non-rapid eye movements (NREM), muscle relaxation, lowered body temperature and slowed heart rate. The body is preparing to enter into deep sleep.

Stage 2: Also characterized by NREM, this stage is characterized by a further drop in body temperature and relaxation of the muscles. The body's immune system goes to work on repairing the day's damage, the endocrine glands secrete grown hormone and blood is sent to the muscles to be reconditioned. In this stage, you are completely asleep.

Stage 3: Still in the NREM stage, this is a deeper sleep still. Your metabolic levels are extremely slow.

Stage 4: In this stage of sleep, your eyes move back and forth erratically. Referred to as REM sleep or delta sleep, this stage occurs at about 90-100 minutes after the onset of sleep. Your blood pressure rises, heart rate speeds up, respiration becomes erratic and brain activity increases. Your involuntary muscles also become paralyzed. This stage is the most restorative part of sleep. Your mind is being revitalized and emotions is being fine tuned. The majority of your dreaming occurs in this stage.

These stages repeat themselves throughout a night's sleep.