Sleep is an amazing process when you think about it. You close your eyes and wake hours later, sometimes with memories of vivid dreams, other times with no memory of the intervening hours. So what really happens when you sleep, what are the cycles you go through?
There are two broad types of sleep that mammals go through. The first is rapid eye movement (REM) and the second is non-rapid eye movement (NREM) and each of these has a different set of psychological, neurological and physiological aspects. NREM is further split into three stares called, inventively, N1, N2 and N3. N3 is called delta sleep or sometimes slow wave sleep.
The sleep cycle is goes from N1-N2-N3-REM and back to N1 again. During a night’s sleep most people will go through this cycle three or four times on average. Generally the N3 stage lasts longer at the start of our sleep and the REM stage lasts longer at the end of our sleep.
It is during the REM stage that most of the memorable dreaming occurs. Delta sleep is the stage in which most night terrors and sleep walking occurs and is also the stage that is hardest to wake from. If you have been sleep deprived then you will have more delta sleep when you finally do sleep.