What are the differences between these?
NREM sleep has limited or no eye movement and seems to be more geared towards overall physical restoration. REM sleep has rapid eye movements, more vivid dreaming, and seems to be geared towards concentration mental refreshment and (perhaps) consolidation of learning).
NREM sleep dominates at the start of the night; REM and NREM 2 only towards the end of the night.
NREM Stages 1, 2, and 3 are literally non-REM sleep. Stage 1 is a transition stage of light sleep. Most of the evening is spent in NREM2 sleep. NREM3 is deep sleep and decreases over the evening (usually disappearing completely after two or 3 sleep cycles). You sleep talk, sleep walk and have night terrors in NREM-3.
REM increases as the night goes on. REM is when you have serial (story-like) dreams.
REM or Rapid Eye Movement sleep is where we dream and a stage in which our body is paralyzed (to protect us). This is essential for mental functioning and recuperation. Despite what some may think (because they can’t recall them) everyone dreams each night. Without REM we would struggle mentally the next day. If we lose sleep on a previous night, we may have longer periods of REM to make up for the lack of mental relief. This is called REM Rebound.
nREM is non-Rapid Eye Movement or non-dream sleep. Our physical body recuperates during these four stages. The landmark stage of n/REM is stage four, or Deep Sleep. This is where sleepwalking, sleeptalking, and bedwetting will occur.