We have an interesting and varied sleep. Even though most of us look pretty much the same all night, there is actually a lot going on beneath the surface.
In 1968, two researchers called Allan Rechtshcaffen and Anthony Kales discovered the different sleep phases and stages. Through a number of different experiments they found out that humans have to distinct phases of sleep. Rapid eye movement, or REM, and non-REM. Non-REM is further divided into four stages. These stages can be discerned by monitoring brain waves, while the two phases can be detected by, you guessed it, whether or not your eyes are moving.
When we first drift off, we go into the first stage of non-REM, then go through stages two to four. After this we slip into REM sleep, where our brain activity peaks and we have our most vivid dreams. We then cycle through this about three more times before waking from stage one non-REM. If we are woken when we are in stage three or four non-REM we will be sluggish and slow for quite a while, so don’t expect much.
The discovery of these sleep patterns has led many scientists to speculate on the true purpose of sleep, as far from being the recuperative function we thought it was for so long, it appears that w are actually very active for much of the time.