Sleep stages 1–4 are collectively called...what?
Sleep stages have been broken down into five different steps. These steps are as follows:
Stage one- This stage is the initial stage of sleep. The sleeper is in between sleep and wake in this stage. In this stage, theta waves (slow brain waves) are produced.
Stage two- This stage is where the sleeper is in light sleep. The body temperature drops slightly and the heart rate decreases as well.
Stage three- This is a transition phase, for the sleeper, between light sleep and deep sleep. Delta waves in the brain are present here (deeper, slower brain waves).
Stage four- Sometimes called Delta Sleep, this stage Delta waves are very active (more so than in stage three).
Stage five- This is the stage where a sleeper dreams. This stage is also known as REM sleep (rapid eye movement).
Stages one through four are referred to as NREM. NREM stands for non-raid eye movement.