SLEEP STAGES AND SLEEP CYCLES We’ve talked a little bit about the different sleep stages. There are about four separate sleep stages. There are three stages of non-REM sleep called 1, 2, and 3, along with REM or rapid eye movement sleep. These from a complete sleep cycle that lasts about 90 minutes each, with each stage lasting about five to fifteen minutes in total length. The first few cycles have short REM sleeps but later on in the night, the REM sleep periods lengthen and the deep sleep non-REM sleep shortens. Stage 1 is the lightest stage of Non-REM sleep. There are slow eye movements and easy arousability. Muscle tone decreases and brain waves slow. This is when hypnic jerks or muscle spasms are most experienced. The sensation of falling happens in this phase. Stage 2 is the first defined stage of non-REM sleep. Slow eye roles stop and brain waves slow. There are brief bursts of brain activity called sleep spindles that are associated with K complexes. These together keep you from waking up. Body temperature drops and heart rate slows. Stage 3 is the deepest stage of non-REM sleep. This is when you get more restorative sleep and you can get slow waves or delta waves. It is hard to awaken the person from this stage of sleep and is when sleep talking, sleep walking, and night terrors usually most occur. REM sleep is rapid eye movement sleep, when most people do a great deal of dreaming. There are rapid eye movements and more active brain wave patterns. It is easier to awaken a person while in REM sleep but it can leave a person feeling groggy when awakening in this stage of sleep. One sleep cycle is the progression through the various non-REM sleep states through REM sleep and finally back again. This lasts about 90 minutes. You do not go through deep sleep directly to REM sleep. It goes from light to deep sleep and back to light sleep before going into REM sleep and starting again. There are no abrupt changes between the stages from deep to light or vice versa.
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