4. Waking up in the Wrong Phase
Human sleep occurs in periods of approximately 90 minutes, and the sleep proceeds in cycles of REM and Non-REM, usually four or five of them per night. The REM phase is the initial and last stage of sleep where the body system begins to shut down gradually, and prepares to wake up, respectively.
The non-REM is a state of very deep sleep. It is divided into three stages; N1 (occurs between sleep and wakefulness), N2 (muscular activities and conscious awareness of the external environment disappears), and N3 (at this point you are dead to the environment). If you wake up during the non-REM stage you are bound to feel tired and unsatisfied, but waking up in a REM phase tends to be more relaxing as the body is already preparing to wake up. However, a complete sleep section occurs in this order: N1 → N2 → N3 → N2 → REM.
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