Sleep affects our daily functioning and our physical and mental health in many ways that we are just beginning to understand. While sleep may seem like a passive, dormant part of our daily lives, our brains are rather busy during this time.

While we sleep our brains usually go through five phases of sleep, stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. The phases operate in a cycle starting from stage one. Once the cycle is complete, it starts all over again. We spend almost half of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.

So what are the stages and what happens during each stage?

Stage one:

This is a light sleep and we can be woken up easily during this stage. In this stage, the eyes move slowly, and muscle activity slows. When woken up from this stage you can sometimes remember fragmented visual images. It is also during this stage where we experience sudden muscle contractions called hypnic myoclonia or hypnic jerks, these are often preceded by a sensation of starting to fall.

Stage two:

During stage two your eye movement stops, and your brain waves become slower with only an occasional burst of rapid brain waves. This is where the body begins to prepare for deep sleep, as the body temperature begins to drop, and your heart rate slows down.

Stage three:

Stage three sees extremely slow brain waves called delta waves that are interspersed with smaller, faster waves. This is known as deep sleep. It is during this stage that a person may experience sleepwalking, night terrors, talking during one’s sleep, and bedwetting.

Stage four:

During stage four deep sleep continues as the brain produces delta waves almost exclusively. People roused from this state feel disoriented for a few minutes.

REM (Rapid Eye Movement):

When we move over into REM sleep, our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increases and our blood pressure rises. If we wake up during REM sleep we are often able to remember our dreams.