Sleep Patterns: what is normal?

So what actually happens when we fall asleep? For most of us, other than the odd bit of snoring, externally there isn't much to see. However, if we take a peek into our brains, we find that things are not as straightforward as they may appear.

Sleep cycles are made up of 5 distinct stages; stages 1 to 4 and rapid eye movement (REM) sleep. Each cycle lasts around 90 to 110 minutes and we typically go through 4 or 5 such cycles each night.

Stage 1 represents light sleep. This is the stage of sleep where you are easily woken. Often people will 'jump' or startle during this period of sleep.

Stage 2 is when your eye movements will stop all together and brainwave activity starts to slow.

Stage 3 is the start of deep sleep. Very slow electrical brainwaves known as delta waves start to appear, showing that the brain is starting to wind down.

Stage 4 is the deepest part of the sleep cycle. There are no eye movements, no muscle activity and only the very slow delta brainwaves. If you are woken up during this stage of sleep you tend to feel pretty groggy and dozy.

REM sleep is the final stage of the cycle, usually occurring after around 70 to 90 minutes of sleep. Everything changes during this stage. Breathing quickens, eye movements start up and become jerky and rapid. In most people muscles become temporarily paralysed and both heart rate and blood pressure elevate. It is during this phase of activity that dreaming occurs.

During the first cycle of a normal night's sleep, the majority is made up of deep sleep, with only a short proportion being made up by REM sleep. As the night wears on we experience less deep sleep and more REM sleep. Often people wake up in the morning during light or REM sleep when dreams are freshest in our memories.

No one really knows the exact reasons for REM sleep, but we do know that many animals also experience similar sleep cycle patterns to ours. The purpose of dreams also remains a bit of a mystery. They are thought possibly to help with learning and brain development, as well as a way to consolidate and organise memories. At the very least they can give you a good tale to share over the breakfast table!