In Stage 1 we drift in and out of sleep and can be awakened easily. If someone is watching you in this stage they would note slow eye movement and low muscle activity. If you have ever experienced sensations of falling or weird muscle jerks in your sleep then you have been in this stage.
In Stage 2 we are preparing for deep sleep. Our temperature drops and our heart rate slows. Scientists notice that our eye movement also stops and brain waves become slower with occasional bursts of rapid waves, called sleep spindles.
In Stage 3 brain waves become very slow (called delta waves), begin to appear interspersed with smaller, faster waves. It is very difficult to wake people in this stage of sleep. It is during this stage that a person may experience sleepwalking, night terrors, talking during sleep, or bedwetting.
In Stage 4 the brain produces delta waves almost exclusively. It is very difficult to wake in this stage and if forced awake we feel quite disoriented.
Stage 5 is the dream stage. Our brain activity is very similar to when we are fully awake and our eye movement is rapid. We experience several REM sleep stages each night.
Part Four in a Five Part Series Part I: The Land of Nod | Part II: The Dark Ages | Part III: All the World's a Stage Buddha described the human mind as being filled with drunken monkeys, jumping around, screeching, chattering, and carrying on endlessly. His teachings...