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Sleeping is not just a shut down from the day, but a highly active process during which the day’s events are processed and our energy should be restored. Sleep architecture refers to the fairly complex structure that makes up our sleeping cycles and patterns during a sleep session. A chart called a hypnogram is used by doctors to summarise these patterns to identify any issues you may have while you sleep.

REM (rapid eye movement) sleep and non-REM sleep. REM sleep is also known as dream sleep and during this time the brain is quite active and blood pressure and breathing can be variable. During non-REM you can also dream, but they tend to be milder dreams and the body and brain is more still and quiet.

Non-REM is divided into four stages, which progressively goes from wakefulness, to light sleep and then to deep sleep. Deep sleep is also known as slow wave or delta wave sleep and this is considered to be the most restful, restorative sleep phase. In a healthy adult, you typically go into deep sleep within 30–40 minutes after falling asleep and then go into a short period of REM sleep. Over the night there is an alternation between REM and non-REM sleep. We sometimes wake during a REM period but typically fall back to sleep quickly. Over the course of the sleep those REM periods get longer and longer until you shift into being fully awake.

The above diagram shows the typical sleep pattern for a healthy adult. You can see slowly as the night progresses you have less and less deep sleep so there is some truth to the idea that the best sleep is had before midnight. Read page 15–16 to find out how drugs like alcohol disrupt this deep restorative sleep.